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Simplest approach for rail sets automation
How would you tackle the automation of a lego rails set. I am looking for a solution that can be achieved with available parts.
From the answer I will chose either to invest into lego rail sets for my son or into digital H0 sets.
What I am looking for:

start given engine and run to given destination, stop.
when approaching a rails crossing stop if segment busy.
change switches for engine to send to destination.
run multiple engines independently and concurrently.

Optionally:

if multiple routes are available sent train to free route.
if train is running low on power send to service station.

I am not interested in setting timings. I want to be able to simply run the different engines each on their own. This requires detectors which are able to return the ID of the engine entering and leaving the different segments.
I'm pretty good at programming and I would appreciate a doable solution running from a computer.

You might also want to check out our question on cost comparison too - although I've seen a video of a very impressive Mindstorms controlled LEGO train set, if it's really an automated train set you're after I'd probably have to recommend a DCC or similar HO set - they're certainly going to be simpler to set up and configure.

I've wanted to do something similar since I took part in a public event last year and we had trains running continuously on separate little ovals. My ambition was to have two stations, each with some switches, and run one train at a time between them and switch it to an empty track where it would stop.
Since I already had two RCXs, my solution was to place one at either station with light sensors to detect incoming and outgoing trains. I motorized the switches (using a modified version of instructions I found online - I could make some instructions if you wish), and wrote a program that allows the RCXs to communicate with each other about the state of the trains and the switches.
There were two tricky parts: one is that although you can send PF commands from an RCX, there is no feedback from the PF receiver so you'll have to resend the command several times and hope for the best. The other is that the communication between the RCXs is affected by the PF commands. When you send a PF command, the receiver in the RCX will end up in a state where the next serial byte is lost, and although there is collision detection for the communication between the RCXs, there is nothing similar for the PF commands (the sending of which requires the disabling of all interrupts on the RCX).
My solution was to design a protocol for communication between the two RCXs such that they, in effect, negotiate whose turn it is to send PF commands and stay silent when the other RCX is sending. This worked very well in my living room, where the trains would happily run and stop and be handed back and forth between the two RCXs (since you can't easily ID the trains, you have to know where they are). I then tried to set this up at an event, but unfortunately the room was anything but compatible with PF. Possibly because of the fluorescent lights, the PF IR range was severely limited and the trains would not receive the signals from the RCXs.
A solution based on NXT (or EV3) could probably be a lot more powerful and reliable, especially since you'll have much better ways of detecting the trains. Even so, I suspect they'd run into the same problems in some showrooms as my RCX solution.

I found that places with white walls work better for IR communication. The fluorescent lights can in some instances completely mess-up with the IR networks, but most of the time when there is no line of sight the signal is transmitted by reflection from the walls and ceiling. A solution a friend uses now is to setup a white ceiling over his installations in large open spaces. The ideal solution would be mirrors, but they are expensive and cumbersome. His preferred solution for shows remains a white waxed fabric. I hope this will help you for your future installations.

LEGO trains are primarily toys, and the recent ones aren't even using metallic rails.
As such, they're usually considered ill-suited for automation purposes. That doesn't mean it's impossible, but it'll prove challenging. In any case, you'll definitely need some computing, so it's good that it's OK with you.
For trains themselves, sticking to available parts will be an issue. PF trains are supposed to be remote controlled via RC and have no awareness of the track of or anything at all. The problem you'll have here si to make sure that whatever signal you send, the train will receive it. Some your RC emitters need to be very well placed, and the bigger your layout, the more this is going to be a problem. Forget about tunnels. And your number of trains is limited, too.
You'll probably need to use a Mindstorms Kit and an IR Link Sensor; the NXT itself can be programmed directly or easily controlled by a computer.
Since you'll be using Mindstorms, sensing trains shouldn't be too much of a problem, either with available sensors (not sure which one would be best though) or by making your own (a reed sensor on the track usually detects LEGO train magnets if there are 2 or more of them together); but you'll be limited by the number of sensors you can plug on a NXT. You can of course use several, or grab some sensor multiplexers. When using Reed sensors, you'll probably hav enough with touch sensor multiplexers.
So far, you see using only standard material (and admitting HiTechnics or other third-party vendors as such) is already becoming a complex solution - feasible, certainly, but not cheap either. And we haven't touched switches yet - not that it's complicated to motorize, but if using NXT motors, it's going to take some place.
In the past, some people have had some success transforming 9V trains for DCC, but I wouldn't consider 9V trains as available any more, and this solution does also require a lot of work and good understanding of DCC and whatnot. I have none of this, so I won't talk much more about it, except to say that this usually doesn't address the problem of switches either, and that you'll need a lot of non-LEGO stuff to make it all work.
In short, I think you can do a lot of fun automation even with current trains, but if you want a complete solution right from the start, LEGO may not be the best suited for that. On the other hand, the challenge of making it work may be a greater experience for you and your son, so I'd advise trying anyway. You can start with simple things, keeping the most complicated things (switches) for later.
One other thing you can do to simplify is make sure that the layout itself is simple. For instance, you can have a single track with a train going back and forth (mimicking the good old 4,5V system shouldn't be hard with a PF Polarity Switch, and that by itself adds a lot of movement to an existing layout, without actually requiring any automation at all.

Thank you for the detailed answer. It brings material to explore and ponder over before making a choice. I will take the time to explore the options. Have you noticed the headphones hat makes your avatar looks like a demon?

Now that you mention it, indeed. I guess I should take the time to make a correct avatar though before worrying about what putting an hat on does to it :-)

LDCC provides a lego solution if you are willing to look for 9V track and modify the motors. There are an endless number of things you can do combining DCC and Mindstorms NXT amoung other things. It really has a lot to do with how much time you personally want to invest. It doesn't matter if it is HO or L(LEGO) scale, they both require a large investment of time to get good results. I have both HO and L scale experience. The LEGO train club I am part of has all kinds of lighting, sound, and action in the exhibits, including light rail that stops at platforms and multiple trains on the same track.
The long and short of it is that LEGO will require more initial investment, but it can do the same things as HO except it is infinitely more reusable. I use LEGO my father used as a child, I am sure my daughter will play with mine when she is old enough. Once something is made in HO, it is very hard to unmake it, but LEGO can be a new creation every day.


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What are all the different ways that LEGO pieces join together?
Has anyone made a list of all of the different types of connections between LEGO bricks?
Obviously there's the stud connection - but there's also the ball and socket joint, the more recent click-hinge, the pole-to-minifig-hand connection, and so on.
I suspect there are a quite a few that are specific to a few pieces (eg door hinges or train magnets). What I'm most interested in though are the connections that are part of the overall 'system'.

It's interesting to note that LEGO is going towards less types of connections; for example, shutters now using a standard clip connection.

There have been attempts in the LDraw Lego CAD systems to do a parts connection database. I'm yet to hear of them getting to something workable.

Currently in use:

Stud and "antistud" (diameter 4.6mm)
Longer studs (Minifig torso)
Minifig legs
Minifig neck and head / accessory (eg backpack) - also compatible with studs
Clip and bar (in a way, similar to stud, but with diameter 3.2mm)
Wheels (3.2mm axles)
Flower connector (similar, but even smaller, present in a surprising number of parts, including spider and Technic chain link)
Technic hole and pin (compatible with studs)
Technic axle and axle hole
Turntable
Click hinges
Ball joint sockets
Brick hinges (I'd wager this one is the next one to disappear)
9v/RC track connection (discontinued)
PF electrical plug (discontinued)
NXT electrical plug (discontinued)
PU electrical plug
Train magnets, embedded
Pneumatic hoses to pneumatic elements and bar elements
Sliding door in grooves
Visors on helmets

Decommissioned:

Flat hinges
12v track clip
4.5V/12v electrical plugs
9V electrical plugs
Train magnets, free (connects to flowers too...)
Tube plate hinge (with red tube)
Wheels (metal pin, as in blue era train wheels)
Wheels (Plastic pin, as in grey era train wheels)
ZNAP
Homemaker arm joints

When you say brick hinges - I presume you mean these - http://www.peeron.com/inv/sets/1133-1.

There are various window / glass / shutter combinations,  door / frame combinations and wheel / tyre combinations too.

...and propellers on shafts, and stickers. Lots and lots of stickers.

Normal, with the studs around the tube
Stud onto tube.
Tile +1 hollow stud to pillar of 1×.
& the edge of a slimbrick between studs. Round 1×1 between studs.
& to pillar (if hole in top).
& some 1× tiles with stud(s) & 5 high have vains, so can take stud midway as well as normal place.

The terms used here are mostly unclear for me at least, can you explain them? Additionally, due to the ambiguity, it is hard to see whether your points are already included in the wiki answer above.

Cylinder = tube, between them, into them. Some pieces can fit to pillar of 1× brick. Some such as steep-sloping 1×2 doesn't have pillars, but another way to hold stud.

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How does LEGO handle the breakage of Hero Factory sockets?
My son has a slowly growing collection of Hero Factory figures, and they have accumulated a consistent problem: socket connector cracking.
The tips of the angular part of the limb which connects to a socket tend to split, causing loose limbs, then eventually a separation of the tip, which causes the limb to fail connection with the socket.

This is through non-daily, low use.  Are there ways to prevent this?  What is LEGO doing to address this?
I've started to notice LEGO (and even Megablocks) using similar ball socket connections on non-Hero Factory  toys, and expect this sort of failure to be common.  I've not seen breakage of this kind through my multiple decades using LEGO.
FOLLOWUP
Per the recommendations below, I've contacted LEGO about this issue.
From LEGO:

I am so sorry to hear (and actually see!) about the broken LEGO elements that you have. Here at The LEGO Group we hold ourselves to an extremely high quality standard. The fact that your elements have broken is something that we take really seriously.
We would be more than happy to send you replacements for these pieces right away. If you would be so kind as to provide us with a little bit more information on the parts, we will be sure to help you out.

After a little research, I let them know the parts were from either Stormer (7169) or Breez (7165) depending on the color, that the other limb ends from those sets were separating in a similar fashion, and asked whether they had noticed similar faults with these types of pieces historically (morbid curiosity).
From LEGO:

Thanks for getting back to use with the sets that you have broken pieces from. I am so sorry to hear that these parts have broken. That is unfortunate. I was able to pull up the image of the parts that you sent with your original email and was able to see the exact pieces that you need. Sadly, these parts have been discontinued and we are unable to replace those parts for you. I do apologize for this. I wish there was some kind of replacement to send, but sadly, there is nothing as a substitute for those parts.
Again, we wish we could help you restore your LEGO set back to new but unfortunately the pieces you need are no longer available through us. There is hope though, Peeron.com is website run by a group of LEGO fans that contains information on LEGO sets, replacement parts, building instructions and more. It’s not affiliated with the LEGO Group but we know from other fans that it has a good collection of older building instructions to download, discontinued pieces to purchase, and great set information.

Ah well, thanks anyway!

You can get those on Bricklink and they can be very cheap to get.

This was a common problem with ball sockets in Bionicle figures released between 2007 and 2010. The first wave of Hero Factory figures, which the pictured elements are from, also used this style of socket, as well as regular bricks with ball sockets released during that time.
The problem has been addressed by The Lego Group, and the new ball socket elements produced from 2011 and onward are much stronger. An exception to this is the 2012 wave of Hero Factory figures, which uses the same style of head piece as the 2010 wave and has the weaker socket (although none of mine have broken yet). However, as of 2013, the figures use a brand new head piece with a stronger socket. As far as I know, the older head is being discontinued like the elements in your picture.
The only advice I can offer about the older style of pieces is to be more careful when disconnecting and reconnecting them. Particularly, when disconnecting the ball from the socket, make sure to pull them directly apart rather than twisting them at an angle to have the ball pop out against the side of the socket.

Yeah, tell that advice to my 6-year-old.  Thanks for your input.  In my opinion, your piece-specific answer trumped the prior answer as it really does address the true underlying question about this particular piece.

Each time I've heard someone from LEGO speak about quality, they tend to insist on on simple message: they can't do anything on a problem they don't know about. This may seem very obvious, but they feel it needs to be repeated anyway.
What this means is that they want every single customer with any quality problem to actually report it. Apart from the fact that they always help customers directly, they record all of it and the number of times a problem is reported is also a good indicator for LEGO that the problem is serious and needs to be addressed.
A simple example: instruction books and sticker sheets regularly ended up bent or damaged. Through the number of complaints this generated, LEGO has learnt about the problem and how seriously it was perceived by its customers. As a result, instructions and sticker sheets are now packaged (manually, I might add, which has an extra cost) in a sleeve with a cardboard to protect them, at least in bigger sets (again, because of the cost).
So, in a nutshell, that's the most important thing LEGO does about all quality problem: they listen.
I have no way of knowing myself if that particular problem of ball joints in Hero Factory figures is very widespread or well known, but the more people report it to LEGO, the bigger the chance it's going to be solved. And in the meantime, everyone who contacts them will get replacements anyway.
So I would advise you to just follow that route: each time you get a broken part, go to the LEGO customer service Replacement Parts page, select "a piece broke while building", type in the set number and select the part which broke. You'll even get a chance to enter in detail what happened. So you'll get a replacement, which solves your immediate problem, but in the background LEGO might learn that this particular part is too fragile if a lot of customers report the problem.
One last thing which needs to be said is that even if LEGO is aware of a problem, or addressing it, or maybe already solved it, it may take time for the solution to reach the public. A new, enhanced version of a part might not appear in sets before the stock of the other version has been used, for example (unless the older version is so bad that LEGO will recycle the stock entirely, of course, but that probably doesn't happen too often).
Note: I apologize if this answer is very generic in nature and doesn't address the ball joints specifically (thus no answers on the "are there way to prevent this" part, although I guess a little bit of soap might help), but I feel it's very important to understand how LEGO deals with quality problems in general.

Thank you for the response, though not the complete answer I was looking for (upvoted!).  I did contact them a while ago via Twitter, as it seems the "go-to" avenue for many who have quality issues with items or prefer a direct customer service response.  I'll try the link and update this question when I receive a response; I am very responsive with StackExchange communique, so I won't keep this question hanging for too long.

I forgot to mention, but can also call them directly (the phone number is on the box, I believe), if you prefer that way - the response will at least be instantaneous. Again, while you can expect replacement parts very fast, whatever effect it might have on their internal production, you'll not be able to see. But a phone call might give you some insight on what they're doing, if you reach someone chatty enough.

There is a Uk version - under Contact Us->Bricks and pieces. I am giving this a go now, and I'll let you know how it went. It looks like they ship replacements with no problems!

Of note, I added an image of the broken parts.

I've had similar problems with other ball sockets.  I posted a picture a while ago about this exact problem: http://www.flickr.com/photos/grandpappy/3988584161/

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I have entered codes for days 1-7 on the LEGO Star Wars Calendar site and now can't enter any more
I have the LEGO Star Wars Advent calendar and have put in the codes up to day 7, however it will not allow me to proceed and put in any more codes from day 8 upwards - are other people having this issue? Can I only "open" so many doors in one day?


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List of prototype or unreleased themes
I recently discovered the unreleased "Seatron" theme as I was looking around for building ideas. After some searching, I also found the unreleased Europa theme which seems to be set in the 1700s and has elements of both Castle and Pirates.
Are there other unreleased or prototype themes and sets?

Brickipedia (A.K.A. lego.wikia.com) list unreleased sets and themes in the form of an article and category of articles. It does mention CYBOTS and Europa in addition to Seatron, although there is no guarantee that the list is complete.
CYBOTS

Contained action figures using both System and the first TECHNIC
  ball joint parts. Several prototype models were created but final
  versions were not made. This theme was made mainly to test the first
  LEGO ball joints, which would be later used three years later on the
  Slizer theme.

Europa

Set in the 18th century. The most likely reason that the theme wasn't
  released is that it was too close to both Castle and Pirates, both
  very similar themes.

Seatron

The theme would have been set on an alien planet, with underwater
  astronauts. Many new monorail parts and colours were made for this
  theme, but when Futuron's monorail failed to make money, development
  of Seatron stopped.

Unnamed prototypes
Here's a space theme using purple and trans neon green from 1989:

And another 1989 space prototype with a distinctive color scheme using both light and dark gray with trans-red elements (dark gray would have been a new color at the time):

Brickipedia has a similar list for prototype sets and themes.


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What is known of the capacities of the MINDSTORMS EV3 when it comes to interconnection with a network (WiFi, bluetooth)
What is known of the new MINDSTORMS EV3 capabilities when it comes to netwoked functions. What type of interface can be plugged to interact with a PC or portable device (smartphone/tablet)?
In term of interconnection (WiFi/bluetooth) and in term of protocols available what are the options?
Are there any libs (C/C++) which are already available and compatible with the brick?

The Mindstorms EV3 brick uses Bluetooth 2.1EDR. What protocol they use on top of that is still unknown, but will probably be released publicly by LEGO at some point. It's likely some compatibility with the NXT is possible (that is, an EV3 and a NXT bricks should be able to communicate together), but this is pure speculation and I doubt they just reuse the exact same protocol without at least expanding it.
For USB, apparently the regular USB port is 2.0, but there's also a host USB port which, according to the previous link, is only 1.1 (which seems strange to me, and the official PDF product sheet for the EV3 brick specifically mentions "USB 2.0 host enabling brick daisy chaining, wifi communication, and USB memory sticks") and can be used to daisy-chain up to 4 devices. The very fact they state a limitation hints that their software itself has this limitation, as I don't see any hardware reason to do so. This means that with an alternate firmware, you can probably do more.
WiFi is only possible using a WiFi dongle connected to the USB port, which seems to be allowed. If the host port is really 1.1, that may limit the speed to 12MBit/s. You can find  its PDF product sheet here which says:
The EV3 Wi-Fi Dongle fits with the LEGO® MINDSTORMS® EV3 platform and uses wireless communication. It plugs into the USB host port of the EV3 Intelligent Brick and provides wireless communication with a computer. A wireless access point is required between the LEGO EV3 Intelligent Brick and any Wi-Fi -enabled computer as well as your Apple or Android device. All you need to do is set up the connection inside the software and you’re ready to go!
Also, considering the OS is linux-based (on an ARM9 processor), and considering LEGO's history of letting people hack Mindstorms in any way they can think of... there'll probably a lot of other possibilities (USB Ethernet, for example).
APIs and/or libraries aren't available yet, and probably won't be until the kit is released, but it seems there'll be at least an official iPhone & Android app to control all robots you can make with the kit.

WiFi Dongle? Great!

Yes, I updated with a link to its product sheet

As I understand it, the existing NXT can't be controlled from iOS Apps, as Apple doesn't allow pairing with untrusted devices. Given that Lego have said it'll be possible to control the EV3 from an iOS, we can presume they've solved this. However does this also mean that third-party (non-Lego) apps will be able to communicate with the EV3 too?

I didn't know about that restriction from Apple - what do they mean by "non-trusted devices" in this context? It it's a matter of approval process, maybe LEGO did the necessary paperwork this time - they do have some iOS apps, so I guess their relation with Apple isn't too bad

The new EV3 Intelligent Brick has the following announced features:

IR sensor
Bluetooth connectivity*
SD Card Slot
USB Port
Linux-based firmware
Full iOS and Android compatibility out of the box

In terms of libraries for connecting with it - if it's based on a standard core, then I would assume that a standard bluetooth stack should be able to communicate with it, but unless it's based around an arduino core we will need to wait until full specs are released before the libraries catch up.
* Assumed based on current NXT feature-set and connectivity for phones.

A bit late but well:
For source code you can check out  https://github.com/mindboards/ev3sources
The EV3 comes with:

Bluetooth, two protocols on top of it, one used by the iPhone App and the other is RFCOMM with application data the same as over USB and TCP.
USB: over HID
TCP: Device uses UDP broadcasts to announce itself and can then be contacted over TCP.

You can plugin a WLAN Dongle into the USB Port or a USB-Ethernet adapter. It was the case that only a particular Netgear dongle was supported. Don't know if that has changed.
Protocol spoken is specified by this manual.
ev3duder, which I wrote as part of c4ev3, tries to detect an EV3 and can send system commands (e.g. Uploading/Downloading) or open a persistent tunnel which you can use to tunnel your own direct commands (check out moveEv3.pl for an example).
If you want to send stuff over USB, you got the ~/dev/lms_usb device file. For WiFi, just open a socket and do your stuff. Bluetooth I can't recall, unfortunately. Check out ev3duder's source for specifics if you don't want to use it directly.


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Is the visual.ly infographic information about the minifigure reliable?
Visual.ly just release this awesome infographic about the LEGO minifigure.
It this all correct information?

Please forgive the length of this but I was careful to check all the facts from the graphic and include source information.
All information in this infographic, except for those that follow below, can be confirmed from the Wikipedia.org page devoted to minifigs:  http://en.wikipedia.org/wiki/Lego_minifigure.  I would not deny that Wikipedia can contain errors, however, knowing the importance that the LEGO group puts on its reputation as a company, it would make sense that they had at least checked the page for blatant errors.  I'm only guessing of course, but as Wikipedia is a crowd sourced tool, well monitored, it can be reasonably relied on for good information.
The following points had to be confirmed through other quoted sources or other articles on Wikipedia.
According to this thread: http://www.bricksetforum.com/discussion/911/production-oddities user davee123 indicates he learned in a meeting at LEGO, by an exec, that the heads were given holes as a safety measure against choking.  Now they have changed that policy in order to accommodate putting the LEGO logo inside the recessed stud.  They apparently felt the hole for not choking had not provided any true safety advantage.
The claim that the Police is the first minifig to have been released is difficult to positvely confirm.  In the Wikipedia page it is noted that the first minifigs were “police officers, astronauts and pirates”.  Hispa Brick Magazine: http://www.hispabrickmagazine.com/en/content/hbm003-lego%C2%AE-minifig-or-life-doesn%C2%B4t-end-30 in its article on the history of minifigs notes that the Police were released in conjunction with “a fire man, a street worker, space figures, knights...”.  The first female minifig nurse is noted to have been released two months after that of the above listed.  This article also confirms that the police officer is to date the most popular and that there are indeed 41 different variations of them.  The article also states the number of minifigs sold per year to be 122 million in accordance with the graphic as well as the claim that with the number of parts there are a possible 8 quadrillion combinations.
This LEGO wiki site: http://lego.wikia.com/wiki/Indian gives information on Native American minifigs being first to have distinct 'racial features', however the drawing on of the nose I was not able to find definitive confirmation of through reliable sources.
The Wikipedia page concerning LEGO video games: http://en.wikipedia.org/wiki/List_of_Lego_video_games lists 43 different games, not 42 though this could be due to a new release after the making of the infographic.  Most release dates for games licensed to non-LEGO media checked out except for the LEGO Indiana Jones which is here dated 2008 instead of 2007.
According to this article at Gizmodo which claims it was created in collaboration with the LEGO Group: http://gizmodo.com/5070884/exclusive-the-lego-minifig-timeline, the 1990 appearance of the ghost is correct with its specialized appearance.  This article also confirms that licensed minifigs began with Star Wars and the character Luke Skywalker, though the infographic merely states “a Star Wars character”.
According to the LEGO Professionals:  http://aboutus.lego.com/en-us/lego-group/the_lego_history/ , the Indiana Jones line license was signed in 2007, though the sets are noted as being released in 2008.  The release of Prince of Persia is also noted as being one year later (2010) than the infographic though does not note the time of contract which may be 2009.   As for the Batman series, I found a website called Brick Superheroes: http://www.bricksuperheroes.com/lego-batman-minifigs.asp which delineates the different Batman minifigs and states the first release to be 2006 as indicated in the graphic.
This article by Cory Doctorow on BoingBoing http://boingboing.net/2012/05/15/history-of-gendering-in-lego.html gives his personal count of gender ratio which he shows in pie graph and states that for the five years he studied he came up with an overall ratio of 3.74:1 but he notes that the first year he took account for, 1989, had its own ratio of 13.5:1.  He does say, “The imbalanced ratio of masculine to feminine minifigs persists today, though it has lessened over time. I have seen several different numbers for this ratio, so I decided to do my own count” which would indicate the ratio shown in the graphic would be difficult to confirm or deny.  I was unable to find definitive proof either way myself.
Wikipedia has this page: http://en.wikipedia.org/wiki/Lego_Homemaker for the Homemaker line which confirms the dates of those sets.
This Wikipedia article: http://en.wikipedia.org/wiki/Lego_timeline confirms the Paradisa dates, but lists the first release date of the Scala line as 1979 not 1997, however, the LEGO wikia page on Scala: http://lego.wikia.com/wiki/Scala indicates it was first released from 1979 to 1980 and then it was re-released again from 1997 to 2001.
The Wikipedia page devoted to LEGO Belville confirms the release year as 1994: http://en.wikipedia.org/wiki/Belville_(Lego).
Wikipedia also has an article devoted to the LEGO Friends line which confirms not only the date but most of the information on the graphic about 'mini dolls' vs. Minifigs.  http://en.wikipedia.org/wiki/Lego_Friends whereas this article: http://www.brickset.com/news/article/?ID=2110 at the Brickset site confirms that according to the fact sheet for Friends, the size difference is 5 millimeters.

Most of the facts and figures are also available in the The LEGO Group Company Profile which has a section on the minifugre. They too state only mention the "first minifigures are launched for the themes "Town, Space and Castle", and also has the "two months after" notice for Nurses.

I'd be mostly sceptical about the sources listed at the bottom of the infographic that apparently come from Wikipedia, Wikia, various blogging networks, and in particular this article published in 2008 from a entertainment site named 'retardzone' which includes no references.

Why would you doubt a source called retardzone?  Sound perfeclly legit.

The infographic is visually stunning, and many of the statements are quite correct.
However, there are a few errors.
For example, the following statements are inaccurate:
Minifigs don't have ears
Some do, for example:

Dobby from the Harry Potter theme
Yoda
Jar Jar Binks
The Lord of the Rings elves

They have a hole [in the top of their heads]
Many modern minifigs don't have this. Some have a recessed stud instead:

1989 Eyelashes... added
It is true that variety was introduced to minifig's faces was added in 1989, specifically in the pirate sets. However, none of these figs appears to have anything that resembles eyelashes.
122 Million minifigs are sold per year
This may have been accurate when the infographic was produced. However, according to TLG, 340 million minifigs were planned for production in 2012. It seems likely that the number of figs sold should approximate the number manufactured, which suggests that considerably more than 122 million are now sold annually.
There have been 42 video game(s) based on LEGO sets
Of course, this has been true at some point, since there are now more than 42 video games based on LEGO sets. However, when the infographic was produced, 42 may not have been the correct number, as the Wikipedia article referenced by the infographic (which almost certainly contained a list of 42 games at the time) is incomplete. For example, it misses out:

LEGO Technic Cybermaster
Rocket Racers, that was exclusive to Legoland, Windsor (now removed).

During my research, I did discover something that really surprised me. According to the infographic, a police man was the first minifig, released in 1978. Now, in 1978 several sets were released which included minifigures for the first time, and amongst these was a policeman. This let me to believe that the policeman was just one of the first, rather than specifically the first. However, in 2003 TLG published an article entitled "LEGO minifigure turns 25". Now, although this article is no longer available at the LEGO website, it is available at web.archive.org, and one of the images on this article was captioned, "Here is the first LEGO minifigure from 1978... ". Unfortunately, the actual image is missing from the archive... but the image is still present on the LEGO web site - a policeman from the 1978 set number 600. So, according to TLG, the first LEGO minifig was, indeed, the policeman! I'm still not sure what this actually means: was he the first designed, moulded, prototyped or... what? Whatever it means, it turns out that the information in the infographic is well sourced.

Maybe by "a hole on the top of their head", they actually mean the recessed stud, which does have a hole in it.

They specifically mention the purpose of being able to breath through it though, and a recessed stud doesn't fit that description.

The 'hole' statement, as far as I know, was true originally but the reasoning behind it must have been revised.


text:
What is different between the EV3 Home and Educational sets?
The newly announced LEGO Mindstorms EV3 sets for home and education have some differences, but it isn't clear to me what they are, specifically.  It seems that have different sensors, perhaps different exotic pieces (like a remote or caster wheel) and possibly slightly different software.  Granted, the sets have not been released, but, what do we know about that is different in the two sets?

Both sets include an EV3 intelligent brick.
Hardware
The Retail (Home) edition (set 31313) includes:

2 large motors, 1 small
1 touch, 1 color, 1 infrared proximity , 1 remote IR beacon

The Education set includes:

2 large motors, 1 small
2 touch, 1 color, 1 Ultrasonic with red LED, 1 Gyro
1 rechargeable battery (battery charger sold separately)

Software
The software for the education version is sold separately to the core set. As well as the programming software, includes datalogging tools, and a firmware version that allows on-brick datalogging.
There is also a difference regarding sensor support: only the education version provide blocks to manage ultrasonic and gyro sensors included in that version. NXT temperature sensor and Energy meter are supported too. And of course, models being different between edu and retail versions, the building instructions that are included in the software are different.
Robots
Each edition includes different Technic bricks and instructions for different robots. You can find a list of those robots at the LEGO Mindstorms EV3 Comparison project, and product pictures on Robot Square.
Parts
The EV3 Expansion Set adds many Technic bricks for even more robots and is suitable as an upgrade for both sets. However, to build all robots officially published by LEGO for either set you need to buy additional parts in any case.
The LEGO Mindstorms EV3 Comparison project on GitHub lists all parts in a spread sheet, tells you which pieces are missing from "education + expansion" to "retail + expansion" and vice-versa, so you can find out which parts (numbers + names) to order in addition.

Do we know if the retail set comes with a castor wheel?

As far as I know, the castor wheel is just a component made up of small Technic pieces. The main part you would need is the actual small wheel, which I do not think is included in the retail set. It's hard to know at this point in time; we will have to wait until the parts list is published

I think the caster is the right-most piece in the diagram of the educational set.  Building casters for the NXT was a real pain, so I'm hoping that both sets include it!

I've made this post into a community wiki. Please feel free to update with new information

Hardware

No

Education EV3
home EV3

1
Intelligent Brick
1
1

2
Large Motor
2
2

3
Middle Motor
1
1

4
Ultrasonic Sensor
1
0

5
Touch Sensor
2
1

6
Color Sensor
1
1

7
Gyro Sensor
1
0

8
Infrared Sensor
0
1

9
IR Beacon (Infrared Remote Control)
0
1

10
Rechargeable DC Battery
1
0

11
Transformer 10V DC
Option
0

12
the number of parts
541 parts
550 parts

13
tray
○
×

Software

No

Education EV3
home EV3

1
Lobby（the main menu of the software）
○
△

2
Programming
○
○

3
Data Logging
○
×

4
Contents Editor
○
×

5
Robot Educator
○
△（assembly diagrams for 5 models）

6
Sound Editor
○
○

7
Image Editor
○
○

Based on this comparison:
https://web.archive.org/web/20140227052442/http://www.ev-3.net/en/archives/98
Some other direct links:

LEGO Mindstorms Education EV3 Core Set brick list - from Lego site
LEGO Mindstorms Education EV3 expansion Set brick list
Lego Mindstorms RETAIL - article

Brickset (check Parts tab):

31313 - EV3 retail
45544 - Education EV3 Core Set
45560 - Education EV3 Expansion Set

Main link of this answer now unfortunately dangling (404).

@Peterino - the link is now fixed.

The web.archive.org link goes to a blank page for me.

@chicks I just checked and the link is working for me. Webarchive needs some time to retrieve old page from archive - please be patient and in case of timeout - retry.

It is working for me now.  :)

There are differences between EV3 Education and Home set including software, hardware and parts.
Software
A slight difference is in the firmware that comes with on-board datalogging capabilities only for Education version
Hardware
The retail version includes a small amount of components compared with educational set, components that include one small motor, 2 large motors, and four sensors (touch, color, infrared proximity, and remote IR beacon).
The educational set includes the castor wheel, 1 small motor, 2 large motors, 2 touch, 1 color and 1 ultrasonic sensor with red LED, 1 gyro, 1 rechargeable battery, and the possibility to download the EV3 software.
Parts
There is a difference of overall 10 elements between retail and educational versions

There are more than 10 elements different between the two versions. A complete list of pieces comparing the two editions and the expansion set can be found in the lego-mindstorms-ev3-comparison project on GitHub.

I received my EV3 educational kit last week.  Yes, it comes with the a rechargeable battery, battery charger, the castor wheel, and a code that permits me to download the EV3 software.  It is disappointing that the educational kit does NOT come with the infra red sensor or IR remote.  Also the educational set comes with approximately 500 more technic bricks than the retail version.

My education core set did not contain a charger or a software download link. If you have a link to download the software, can you help send it to me or post. Thanks

I am planning to buy one for myself( age: 25+) , I am gonna buy it for first time and education set looks more appealing to me ( Gyro, 2 touch and more parts). Please suggest which one I should buy then

Edu set comes with fewer technic pieces (not "500 more") than the retail version.


text:
How to improve the range of an IR receiver?
I am creating a new Truck which contains two IR receivers in the front hood.
With my testing I get a range of about 6 feet (I have also noticed the small Technic motors on the IR receiver are slow when as the distance from the remote increases) until the receiver losses connection.
Is there a way to improve the connection and make the range bigger so my truck can go further than 6 feet?

Do you mean Truck instead of Trunk? And which motor are you referring to when you write "motors on the IR Receiver"?

Soory I didn't even noticed that typo :)

And the moter is the small technic motor.

Fresh batteries may help, too - ever noticed how TV remotes tend to exhibit the same behaviour with worn out batteries?

The best options to improve IR reception is to actually modify both the receiver and the remote (though the remote is more important to upgrade than the receiver).
Common modifications include replacing the transmitter/receiver element with higher range/power components (this may be at the cost of space), or adding reflectors behind the elements  to better send/capture the IR signal (aluminum foil works as a great DIY reflector for closed spaces.


text:
What would be a simple trebuchet design at the Minifigure scale?
I would like to have a trebuchet design at the Minifigure scale and simple enough for kids 10+ to build.

Note 1: The counter weight can be any non-LEGO heavy object.
Note 2: On top of the standard LEGO bricks, we have a lot of LEGO Technics and my kids are using them all the time. So, Technics are OK in the design.

I assume you're happy with a non-LEGO weight? Most elements are quite light unless you've got a few weight bricks lying around?

@Zhaph-BenDuguid Good point. I'm adding this to the question. Thanks!

Does it need to be functional?

Just as a bit of information, minifig scale isn't terribly restrictive as a trebuchet can be relatively massive compared to people. http://en.wikipedia.org/wiki/File:Trebuchet_at_Warwick_Castle,_2009.jpg

@jncraton That's right. That gives more freedom for your design.

@Joubarc Off course it needs to work.  We have a castle to attack.

@Ambo100 No specific problem. I could build one and I could also design one for my kids.  I'm looking for other design(s) and (most probably) get really good ideas out of them. My kids and I will build 4 or more and it would be cool to have different ones.

I occasionally use the rubber wheel tires for small weights. They work pretty well if you need something kinda heavy. I don't know if you want to use them 'cause they don't exactly look super pretty...

If you don't need to worry about aesthetics, you could also use a small battery box

The set Knight's Stronghold includes a functioning, if dinky, trebuchet.

There are a number of designs on the net that I found with a simple search. Google image search produces images from the merely functional ones like the instructions linked here through to quite realistic looking ones that appear likely to work.

or this big one

The key for a simple, easy to build one is to use wheels on the base. It will shake back and forth when fired which means the structure does not need to be as strong. If you don't do that then the base will need to be similar in size to the arm, as in both pictures above. I am a little surprised that there's so little bracing on the arms of these models, as you can make a much stronger model using a tension member at least on the top of the arm, if not below.
But with Lego the main issue will be the density of the weight. Lego doesn't do high density part, so most people use non-Lego weights. Since you're willing to do that it's easy - the first picture shown has a lead weight, which is why it's hard to see that there's a weight at all.

You could probably still pull off an official-pieces counterweight with the right size battery piece; there are several in Lego's history that are rather hefty and would adequately fill that role, and many of the physics training aid sets I've seen include them for the purposes of training motor-based construction functions.


text:
A piece with no place in Heartlake Stables
I recently bought this set for my niece for her birthday, when we were finished setting it up we noticed a larger orange piece that we couldn't find a place for but was in the set and in the back of the book where it outline what pieces there/how many of them. I just wondering for sure what the piece goes to?

Since you found the part in the booklet, could you specify its number as well?

Nevermind, I'll go and assume you're speaking about 4654448

That part is the new Brick Separator which LEGO includes in most bigger sets:

It's not part of the construction itself, but is a tool to allow you to easily disassemble constructions. You can compare it with the older version in this question on how to separate 1x2 plates.

Oooh, I hadn't seen the new one. I like the introduction of the + peg; I always had to fish out a + rod for pushing those out.

Page 3 of book 1 of the instructions.


text:
Are there any Star Wars vehicles that have not yet been produced in a Lego kit?
This includes all six films and the Clone Wars spin-offs.  Every vehicle I can think seems to have been produced as part of a kit at some point.  Are there any that haven't?

Did you read Wookiepedia? All of it?

But, all joke aside, LEGO is likely to focus on visual Star Wars rather than obscure expanded universe reference, so I can see why you restricted your question to the films and Clone Wars.

Actually, there are some sets that take place using expanded universe that LEGO did make, such as the sith sorceror/warrior ship from the old republic.

@CBredlow There's quite a few more then that

EU sets seem to mostly be based on (Old Republic) video games

@bungeshea Ah I forgot about the Rogue Shadow! Need to buy that one. Given enough Lego, anything in possible.

Wikipedia has List of Lego Star Wars sets.

CapnRex has started a series on what's missing, and an interesting take on why those sets might be missing over at BrickSet: http://brickset.com/news/category-What-s-Missing

As far as I know, all of the most common vehicles have been produced, but I could be forgetting something. There are many obscure vehicles which have not been produced, but I don't see any reason to try to list them all. Some examples would be many of the pod racers from Episode I, many of the hundreds of vehicles shown on Coruscant, or several of the speeders seen in the Mos Eisley approach in Episode IV.
The most notable vehicle that I can think of that has not been produced to my knowledge are the Royal Cruisers from the prequels:

Update:
I had previously been mentioned the Nebulon-B Frigate featured in Episode V and VI:

The Nebulon-B has now been produced:

Not that it hasn't been made in LEGO by fans - and there's a (smaller) one on Cuusoo too. But seeing the fragility of the center section (seriously, who does design spaceships that way?), I'm not sure LEGO would be willing to make an official one. It's not so much swooshable as explodable.

There hasn't been too many of the rebel cruisers (i'm lumping all of the ships larger than a fighter together) made by LEGO.  THere's that one transportish ship they take from Hoth that wasn't used.

The podracers are an obvious one, I should have thought of that.

@Joubarc, depending on the scale you're building at, I can think of a half-dozen ways of reinforcing that center section.

There are quite a few:

The Naboo silver cruisers - I think there were three in all - none produced.
Several speeders in Episode II, all seen in the city and several transporters too.
The Jedi speeders, some have been made, but not in all the colours seen in the movies.

And as for the clone wars series, the list becomes lengthy...

The ones from the original 6 movies and that should have been made:

Naboo queen silver cruiser from episode 1 (with queen handmaid fig(s)!)
Clone quadrans (if I'm naming them correctly) from episode 2 (the guns taking down a Trade Federation ship)
Rebel transport shuttle from episode 5 (escaping Hoth) and 6
Rebel medical frigate from episode 5 and 6
Mon calamari cruiser

Very optional in my opinion:

Trade Federation admiral ship
Trade Federation transport ship
Separatist cruiser from the opening scene of episode 3
The two other Naboo cruisers
A Uta Pau shuttle seen on two or three images (and natives from the planet in the set please!)
A clone tank seen on two images on a bridge under snow in the order 66 scene

Not ships, but still should have been made:

Gungan city (and, why not, one big creature carrying their shield generator and one of their catapults)
A Jedi Temple?
Kaminoans!
Geonosis arena beasts
One of the Skywalkers house?
Republic Senate with Sidious and Yoda fighting
Bizarre blue/purple creature on which clones are riding on Felucia (order 66 scene)
Mustafar locals (humanoids and lava beasts seen on one image)
Asteroid field locals sheltering Padme at the end of episode 3
Bantos... Bantas... Ban... you know the big hairy thing the Tuskens are riding in episode 4

Millions! Separatist War Ship,UT-AT, Republic Assault Ship, Umbara Military Canon, and many many ships from the Clone Wars TV show (From Arc's this season mostly)

TPM: Trade Federation Battleship, Trade Federation Landing Ship, Naboo Royal Starship, Coruscant Air-Taxi
ATOC: H-Type Nubian Yacht
TCW: Trident Drill Assault Craft, Umbaran Starfighter
ROTS: Separatist Cruiser, The Invisible Hand
REBELS: Imperial Interdictor, Mining Guild TIE-Fighter
RO: AT-ACT, TIE Reaper, The Profundity, Hammerhead Corvette, Zeta-Class Imperial Shuttle
ANH: pretty fleshed out
TESB: GR-75 Medium Transport, Nebulon-B Frigate
ROTJ: Mon Calamari Star Cruiser
TFA: pretty fleshed out
TLJ: First Order Dreadnought, Canto-Bight Police Speeder, The Raddus, The Supremacy

Banthas! That to me is the largest oversight in Lego's portrayal of the original movie so far.  This is made even more baffling with the upcoming release of a "Tatooine battle pack" that comes with yet another Tusken Raider...missed opportunity there!


text:
List of Helpful Websites for Beginning Collectors
I recently wandered into my father's basement where my brother and I used to have our "game room" setup. I stumbled across a massive amount of LEGO that we had collected over the years.  Since then, I've had the urge to get back into LEGO, taking a more adult approach at collecting them.
I was wondering if there were additional sites besides the one's I've found that may shed some light for a beginning collector.  Also, feel free to include any tips that you think may be beneficial in this quest! Here are the list of sites I've come across:

http://www.lugnet.com/
http://lego.wikia.com/wiki/LEGO_Wiki
http://www.brickset.com/

On top of the already mentioned:

http://www.lugnet.com/
http://lego.wikia.com/wiki/LEGO_Wiki
http://www.brickset.com/
http://www.peeron.com - Large set database and instruction scan library
http://www.bricklink.com - Lego marketplace selling millions of used and new parts and sets. This is also a nice reference for information and
inventories related to old sets.

I personnally use the following ones as well:

http://www.brickfactory.info/ - Online collection of Lego Sets instructions
http://rebrickable.com/ - Site allowing you to see what other Lego set you can build from your existing collection

After that, it all comes down to forums and more specialized websites that directly depend on your area of interest (sci-fi, military, castle...), your language, and your location.

On top of the resources that you listed, I have found these two sites to be incredibly useful:

peeron.com - Large set database and instruction scan library
bricklink.com - Lego marketplace selling millions of used and new parts and sets. This is also a nice reference for information and inventories related to old sets.

It's not a site, but if you don't mind books, I would recommend The Cult of Lego by John Baichtal.
You also might be interested in finding a LUG (Lego users group) near you. Here's a map.


text:
Is Mindstorms EV3 backwards compatible?
LEGO Group announced the next Mindstorms version, the EV3 which will be available in the Fall, 2013.
Does anyone know if the new version, specifically the controller, will be backwards compatible with the NXT 2.0 sensors and motors?
I'm assuming all of the other parts are standard Technics parts and should inter-operate without a problem.

The LEGO Group have advertised the EV3's excellent backwards compatibility with NXT.
As the cables are the same, the EV3 will work with NXT sensors, motors and, of course, LEGO Technic bricks. RCX sensors will work with the aid of converter cables.
Software designed for programming the NXT will not work for the EV3 as the NXT runs firmware, but the EV3 runs Linux. However, the graphical software that ships with the kit will be able to program older bricks.
From the official EV3 FAQ:

Q: Can NXT sensors and motors be used with the EV3 P-brick?
A: Yes. LEGO® MINDSTORMS® EV3 uses the same LEGO® TECHNIC elements and RJ12 connector cables as the MINDSTORMS® NXT, so all your existing sensors, motors and building elements will work  with the new platform, and the software will recognize them as NXT sensors/motors when they  are plugged in.

do you have a link for LEGO Group's statement of backwards compatibility with NXT?

I do not think that TLG have actually announced it on their website, but all of the articles on tech blogs say so. (The tech blogs have received their info from LEGO's announcement at the Consumer Electronics Show in Las Vegas.) This guy who was invited by LEGO to beta test the new product says so on his blog

Ah, LEGO have just released an EV3 FAQ page that confirms these facts

Also, have a look at this article on Robot Square about EV3 and NXT compadibility.

The EV3 will run old sensors, motors, and lego bricks. I am sure it will run NXT 2.0 and NXT 1.0 motors, sensors, and etc. but not sure for RCX.

It should be possible to run use some elements from the RCX system by using a converter. See: Can I use RCX sensors and motors with the NXT brick?

Some parts will be compatible with the EV version while others aren't. You can see a complete list with compatible parts in this article http://www.intorobotics.com/building-robots-lego-mindstorms-ev3-features-programming/.

This is not true in my experience! The NXT touch sensor is not detected by my EV3 with the latest firmware. I have tried the NXT touch sensor on the EV3 and it is NOT compatible. Since I have a few of these and really want to use them on my EV3 I investigated it further. The NXT sensor switch connects a 2k2 resistor between pins 1 and 3, with all other pins unconnected. The EV3 sensor is much more complicated, but the main difference is that it switches the 2k2 resistor between pins 4 and 6. I converted the NXT sensor to be EV3 compatible, by removing the existing 2k2 resistor, shorting pins 3 and 5, adding a 910 ohm resistor between pin 3 and 1, and changing the switch to switch the 2k2 resistor between pins 4 and 6. It is now detected and works fine. Why this sensor isn’t compatible I’m not sure, but the EV3 input ports are definitely different from the NXT to some degree. Looks like the intelligent sensors work though, as I can use the NXT ultrasonic and light sensors. Waiting for the EV3 HDK to investigate further…

Have you contacted the Lego Group through their support center?  I would start there, especially since they have advertised sensors as being compatible.


text:
What does EV3 stand for?
I am wondering what the official reason behind the name of LEGO's latest MINDSTORMS robotics platform is. What does "EV3" stand for?

From the official EV3 FAQ:

What does EV3 stand for?
This is the third generation of the LEGO MINDSTORMS platform and the
  "EV" stands for evolution, hence EV3.

The first two generations referred to here are LEGO MINDSTORMS RCX and NXT, respectively.

...and presumably the number 3 comes from the fact it's the successor to NXT 2.0?

@Ambo100 No, I don't think so. EV3 is not NXT, it's a completely different line. See this post on the Mindboards forums and all following posts for more info

@Ambo100 I'm not sure the numbers are incremental in that way - NXT started back at "1" effectively after versions 1, 1.5 and 2.0 of Mindstorms Robotics Invention System, so the 3 really comes from the fact that it's the 3rd generation (RIS, NXT and now EV3).


text:
What are the known software tools for the EV3?
The EV3 is coming in Fall/Summer of 2013 and we tons of unknowns that will come in EV3. I am curious what software EV3 will run and will older generation software run on EV3 (NXT 1.0). And my final Question EV3 will work with Apple and Android devices, so that would mean iOS and Android developers could make application for EV3 or will only Lego make apps for EV3.

As you say, there are still tons of unknown at this point, so asking the question is way premature.
However, considering the software is said to be based on the same technology as the one in the NXT, it's likely it won't be too different, and that's why that software will be able to control NXT bricks. However, I also doubt you'll be able to control EV3 bricks with NXT software.
That software is going to work on Mac OS and Windows (not 8 or 8.1 rt); it's likely the apps for Android will not be a full-blown development environment (although, it's just a guess, it would be way cool if it was).
As for third-parties, LEGO has been very very open about its software in the past, and they will be this time too - opening the door for a plethora of applications/firmwares/whatever on several platforms.

The mobile apps will only be able to control the robot, perhaps remotely execute programs, nothing much more then that I think

But the beauty of it is, how long before a fan creates his own app to do just that? It's certainly doable in some way, even if not fully mimicking the LEGO software

Yep - I'm looking forward to loads of iOS and Android apps which have innovative interfaces allowing people to control, receive data from, and even program their EV3 bricks.

The graphical software that ships with the EV3 set can program both EV3 bricks and older generation bricks. We assume that this means NXT 1.0 and 2.0 bricks. However, it is unlikely that NXT-G will work with EV3 bricks as EV3 bricks run a custom build of Linux, whereas older bricks run a custom firmware.
LEGO will create an offical app for both Apple and Android devices, but other app developers will be able to use the API to interface with the EV3. There will most likely be some documentation available (as it was for the NXT), and perhaps a SDK available for download.

NXT bricks, yes, but you can pretty much forget about the software being able to program a RCX brick

@Joubarc Sorry, I meant NXT 1.0 and 2.0 bricks. Although, there's really no difference…

Indeed, none whatsoever as fara s the brick is concerned


text:
Which brands (fictional and non-fictional) have appeared in the Town/City theme?
A few years ago I wrote an article about the fictional organisation logos found in the City theme.
I'd quite like to revisit this, as I'm sure I must have missed some. I also only focused on the fictional brands, but I know some licensed brands have appeared too.
My current list is:
Fictional

Police
Fire
Hospital (Star of Life logo)
Postal service (envelope and bugle icon)
Railway (double arrow logo)
Refuse / recycling agency (eg 4206)
Highway maintenance agency (motorway icon) - eg 6653 and 6521)
'Octan' (oil/energy company)
'AirLine' (now uses the bird logo)
'International Transport' (eg 161 and 6367)
Cargo company (yellow box on blue world logo) - eg 4551

Real

Shell (1966-1980, before Octan was introduced, e.g. 1256)
Ferrari (eg 8673 - part of the 'Racers' theme but minifig scale)
Toys R Us (7848)
Maersk (1552, 1831, 1651, etc)
Deutsche Bahn (eg 7735)
BNSF (Burlington North Sante Fe) eg 10133
Lego (eg 4549 and 10156)
Exxon (eg 6679 6375)
Danone (only once - 1591)
Color Line - eg 2149

Are there any others?

I suppose NASA would be on the outskirts of the Town/City theme, but there it is...

I can't believe that nobody else else has posted the most important real company that appears within the LEGO City theme... the LEGO company itself!

There is a good list of promotional sets on Brickipedia, that includes the set theme. Many of the town / city sets include logos or brand names of real-world companies.
Other sets that include real-world brands (some of which don't count as Town / City, according to the Brikipedia themes list) include:

Esso appeared on some very early sets.
DB (Deutsche Bahn) appears on various trains, including 7725.
Sports sets such as, 3432 which has NBA logos on the player's chests, or 65221 that included a Spalding basketball.
1656 Viking Line cruise ship.
Interfrigo, set 147.

Of course! How did I miss that? Set 10156 seems like the most recent example I can find, but I'm sure there are others. I've added it to the list in the question.

Didn't think about LEGO either, I guess it was too right under our noses.

I have a very old set with the word "Legoland" printed on a Brick. So that's another

Here are some additional non-fictional brands and their set(s) under the Town theme:
Chocomel (Nutricia), Holland
Chocolate Factory
Canada Post
Mail Van
Mail Truck
ANWB (Breakdown service), Holland
Breakdown Assistance
Roadside Recovery Van and Tow Truck
UNICEF
UNICEF Van
Touring Club Schweiz
Breakdown Assistance
Air Canada
Air Canada Jet Plane
MD Foods (Denmark)
Milk Truck
Emirates
Emirates Airliner
Arla (milk supply company, Sweden)
Milk Delivery Truck
Renault
Racing Car
Velux
House with Roof-Windows
Color Line
Container Lorry
Tine Dairies (Norway)
Milk Delivery Truck
McDonalds
McDonalds Restaurant
Also there is the 'Houses' set from Weetabix. This doesn't actually include the brand in the Town set itself, but includes the pieces to build a Weetabix figure in the set and is part of the Town theme.
Under the City theme:
Vestas
Vestas Wind Turbine

Lego also collaborated with several airline companies to release a standard plane but with stickers denoting the airline name. I remember excitedly purchasing them back in the day. They were only available through their in-flight shopping if I recall correctly. I have two. One is El-Al and the other one is for a Japanese carrier (need to check either ANA or Japan Airlines).
Here is the link to the "generic set" although it is labelled El-Al.
http://www.brickset.com/detail/?set=4032-3
You can actually see the whole set of airlines here:
http://www.brickset.com/browse/themes/?theme=World%20City

Real brands include:
Mostly it's the three early Maersk Trucks - 1552, 1831 and 1651 that are usually listed under the Town theme.
Toys R Us also appeared on one City themed truck
Outside of the Town/City themes but still minifig scale you then have:

Maersk Train - under Trains.
SNCF - In it's old orange livery is the basis for the Horizon Express train under Creator.
Ferrari - Is usually listed under the "Racers" theme rather than Town/City
Porsche - In the 2015 LEGO Speed Champions line
McLaren - In the 2015 LEGO Speed Champions line

Other brands have also appeared in other more advanced/non-minifig scale themes, such as:

Boing - The 787 Dreamliner.
Maersk (again) - The Sealand Container Ship
Sopwith Aviation - The Sopwith Camel.
Volkswagen - The T1 Camper and Beetle

Don't you mean SNCF?

I don't think any of these have been in town/city themes

Thanks, I've updated the question to add Maersk to the list, and also to note that Ferrari wasn't technically part of City (though I've kept it in as it's clearly compatible).

The Horizon Express is clearly inspired by the SNCF early TGRs, but as it isn't actually identified as such I've left it off the list.

I wouldn't consider "hospital" as fictional.
At first, LEGO did seem to use the Red Cross logo, but they have since then had to stop (presumably because of the Red Cross being very protective about their logo). Note that the logo they have been using since isn't fictional either.
12v era trains provided stickers for a lot of different train companies, I'm not sure if what they use now is fictionnal or not (I think so)

You're right about the 'Star of Life' not being entirely fictional. Although it's also not solely owned as an identity of any particular real-world organisation as I understand it, so it's arguably more of a generic symbol. Oh and I'd forgotten about the early Red Cross bricks!

Those 12V train stickers are interesting - they definitely include some real world companies (including British Rail and the Danish State Railways). Were any of those ever produced as printed bricks, I wonder?

Depending on how you classify "Town/City", you might want to consider these:
Real

Mini Cooper big, small
Nasa (several parts)

Fictional

Ghostbusters 21108
Gringotts and other Harry Potter brands 4714, 10127
The smiling minifig coffee cup part


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does Lego make bricks with a stone, brick or concrete block design?
Does Lego make the bricks with a stone, brick or concrete block finish on the sides?  I would like to use these for walls and buildings on a train layout. Thanks!

As usual with LEGO, the best solution is often to make your own.
You can make quite impressive brick walls using tiles, like this (image from Brickshelf):

There is a tutorial for something similar here.
A range of other techniques can be found in an article called Avoiding the "Big Gray Wall" Syndrome  at Classic-Castle.com. In fact, Google LEGO castles for a great source of inspiration for stonework of all kinds. For example, check this and this out.

Even when simply placed next to another, tiles give a great effect, thanks to the bezel. Check this house for a basic example

The gaping and color of the "Bricks" give a good allusion that its looks like a Brick Wall.

Related: How can I add additional detail to large walls?

That looks like the pieces that have knobs on the sides are used for the walls, then flat plates are placed on the knobs.

There's this part, which has a brick pattern molded into the side:

http://brickset.com/parts/?part=4646577

Since the brick was produced (some time last year) it can be found almost everywhere, it's already appeared in many official LEGO sets and MOC's and it's getting cheaper over time

They're fairly widely used in the 'Friends' series

In short: Yes.
There are actually quite a lot varying in base colour and stone/brick design.
As mentioned by another poster, many are from the castle theme, but there are also interesting ones from Duplo which may help with your layout if you are trying to cover a large area as the Duplo blocks are larger.
Some examples are below, but for lots more take a look through these items on Bricklink.

Brick 1 x 6 x 5 with Stone Wall Pattern

Panel 2 x 5 x 6 Wall with Red Bricks Scattered Pattern

Panel 2 x 5 x 6 Wall with Scattered Stones Dark Gray Pattern

Panel 3 x 3 x 6 Corner Wall with Scattered Stones Light Gray Pattern

Duplo, Brick 2 x 2 with Stone Wall Pattern

Duplo Building Wall 1 x 8 x 8 with Window Opening - Castle

I'm pretty sure some of the Castle series have tall pieces with some brick outlines...


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Is there an easier way of threading Technic pins into other elements?
I've been using Lego Digital Designer to recreate a few models I've built in real life. One model in particular uses many Technic axles which need to be inserted fully into other Technic bricks (like the [part:32014] shown in the image below).

(Click image for animation)
If Technic axles aren't inserted all the way, it causes more problems later on in the build, when the same group of parts are duplicated and used elsewhere.
In some cases, moving the camera angle around can help, but the axle continues to flicker around the screen as the axle is inserted.

As someone who also argues with LDD occasionally, have you tried using a placeholder technic beam to get two connectors at the right distance and then adding the axle into both connectors before deleting the placeholders?
If the placeholders are in a different colour from the rest of the model, you could use as many as you need and then delete them with the Colour Select tool, leaving just the parts behind.

One possible solution, but I can't tell if it would be easy, might be to edit the .lxf file yourself to check/correct the position of the axle.
Unfortunately, I'm not sure there is much documentation on the subject; at the very least I think the .lxf extension is just a zip container, so changing .lxf to .zip is the first step. (of course, backup the whole file first...)
Considering there are ways to convert files between LDD and LDraw, I would tend to think it's possible somehow. You could also convert the file to LDraw and check/correct the axle position within an LDraw editor (they usually give you the coordinates somehow, and at the very least you can check the .ldr source easily as it's text-based). You could also use LDraw altogether, if you find out it helps you place parts (maybe it would).

Maybe I forgot about the "easier" part of the question, though


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LEGO Digital Designer Alternatives
I am been using LDD (LEGO Digital Designer) for my latest NXT project and noticed a major delay in building and making instructions for my Projects (My Mindstorm projects contain well over 500 pieces) and the instructions look all weird for my big projects. And LDD is discontinued so I doubt LEGO will make an EV3 update.
I am curious if you guys know any paid or free software that allows you to make projects for LEGO (Mindstorm). I am looking for something fast, (optional) that will work for Mac and PC, have animation to present my projects, and finally make instructions for my projects.

This is probably a duplicate of Good LEGO CAD Design Software with Technic elements and animation

"And LDD is discontinued so I doubt Lego will make an EV3 update." The DESIGN byME service was discontinued January 2012, but I believe Lego Digital Designer is still being supported.

There are several editors which are based on the open LDraw part database.
I believe that the most popular are MLCAD and LeoCAD. I personally use LDD, so I can't speak to the quality of the instruction generation from these tools, but they do at least offer the ability to create instructions.
LeoCAD is probably your best bet for doing animations, and it is available for Windows, Mac, and Linux.
BrickLink has recently released Stud.io in open beta, and it appears to combine the best of LDD and LDraw - it works with the LDraw part database but will import LDD models and offers a similar interface to LDD as well as collaboration and integration with the BrickLink shops for purchasing the elements for your models.

Not exactly an answer to the question, more an answer to the tile of the question:
For a much more lightweight alternative, check out the new LEGO designer from google.
http://www.buildwithchrome.com/
It only works in Goolge's Chrome browser as it is essentially an experiment to show off Chrome's WebGL capabilities.
There is no download as it is completely browser based and it also gives you an easy way to share your builds with other users and view builds for other users around the world.
Using location tagging you can actually place your build on a specific area of a google map and see your creation rendered in 3D in place.

As of Jan 30th, 2017, http://www.buildwithchrome.com/ no longer allows addition of new buildings - it is essentially read-only now.

As of March 2019 the site is closed.

SR 3D builder is another good alternative I like to use, it uses the Ldraw parts library, but has a more intuitive connection system than MLCad, without the connection restrictions LDD has.
I don't know that SR 3D builder supports mac, but I believe it fits your other requirements nicely.

There is also another solution called Mecabricks which is online based and works with WebGL. Therefore, you only need a browser to start building or check the 3D models already published by the other builders. However it is not compatible with LDD or Ldraw and part library is different and doesn't include as much parts as the others yet.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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How to Make a Lego Claw Arm?
I am trying to build a lego claw arm to pick up stuff that is out of my reach and I need some ideas on how to design it. I would like a mechanism to be able to open and close the claw from the opposite end of the arm.
I'm not looking for an arm design which can extend. I would also like ideas about fixed-length arms. Also, I have many, many different TECHNIC pieces. Designs can be very complex and they can use large numbers of pieces.

If you're after a simple collapsible solution to reach those items just out of reach, you can start with the following setup:

You can extend this for quite some way, and use longer bricks or beams throughout if you wish.
To finish it off, I'd use a couple of longer bricks with some additional plates on the end to act as fingers, and add some handles (via axles) at the bottom. If you use longer bricks at the ends then the middle pin would need to be offset from the centre to keep it smooth.

It's a time-tried classic

Yes. I have tried that but I would like ideas more how to make the actual claw and how to make it open and close. Also the claw needs to be pretty sturdy and it needs to have good grip.

I built a similar model to Zhaph's claw arm but with beams and a basic claw attachment:

360° Animation, Demonstration Video
I had a few problems operating the claw when I built it again with real bricks. If you collapse the beams too far, it can be difficult to open them again. When you try to pick up items with your tool, you also have to anticipate just how far the tool extends (try and possition the claw as close to the object as possible, the beams will push the object into the claws).

Well... I guess that would work... But I don't really like the part where to grab something it has to extend even more.

@J.Walker I've built another model claw that doesn't extend, but it's not as reliable as the extending claw (and requires many, many more pieces). I'll see if I can make any more improvements before I share the design.

I would prefer a different model from this to demonstrate a claw but this is good to. A three fingered claw would be a better model for a robot but this is the perfect model for a non-robot claw it's cool!

If you don't need the arm to be extendable then you might get some ideas from the various Technic sets that feature cranes or claws, like the 8868, 8479, 8436, 8110 or 9397.
These offer multiple alternatives, as in pneumatical or purely gear-driven solutions, can be scaled up with appropriate supports and mounted on your own arm designs.


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I need help with a broken LEGO motor
I have a LEGO motor and it broke but I didn't know why so I took apart the LEGO motor to see if the wires were the problem.  I tested the wires to see if they were working but they weren't and I can't find where they are broken so any advice on what I should do?

What type of LEGO motor do you have? Also, what do you mean by 'it broke'?  Does it turn slowly or not at all? Can you turn it by hand?

PF large motor.

The easiest solution, provided that motor is still in production, is to contact the LEGO customer service using the "broken part" button, or via telephone directly which might be easier for a part such as a motor.
They'll usually provide a replacement without problem, but be advised that by opening the motor yourself, you probably voided any sort of warranty and may need to pay for a replacement.

Hi your link is not working for the form. I also have a a motor (large) thats not working

Indeed, LEGO changed their website a while ago, which means the link I provided isn't working anymore. Try https://www.lego.com/en-gb/service instead.


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What colors does the NXT Color Sensor support?
Quick question, what colors does the NXT color sensor support? Is it the entire rainbow or only specific colors?

It depends on which version you're talking about.
NXT 1.0 Light Sensor: This sensor should detect up to 100 shades from white(100) to black(0).
NXT compatible Hitechnic Color Sensor: This sensor will detect 17 colors including white(17) and black(0) or 100 shades from white(100) to black(0).
NXT 2.0 Color Sensor: This sensor can detect 6 colors including white(6) and black(1).
To complete the list (even though it is not backward compatible with NXT) -
EV3 Color Sensor: This sensor can detect 7 colors which are the same as the NXT 2.0 sensor plus “No Color”?  Yes, according to LEGO's website, this new sensor can detect when there's no color.  Does this means white or that the detector is not sensing a color?  This needs to be validated too.
This is one area where, as new versions are coming out, the possibilities of the sensors are diminishing.

So I should try to find an older model? Seems kind of silly they would remove functionality... Is there then an advantage to even using the second model? Faster speed / detection, faster data transfer, or is it same but with less color support?

This simplification is probably is link to two factors: the sensors design itself and (most probably) keeping it simple for the target users.  Do you need a wide range of color sensing?

It would help but I figured out a way to reduce the colors needed. Thanks for your help!

The EV3 sensors are not compatible with NXT. Only the motors are. http://mindstorms.lego.com/en-us/News/ReadMore/Default.aspx?id=476781

The NXT 1.0 sensor is a light sensor, it does not differentiate colors - only 100 shades of light. The 2.0 sensor can be used in "raw" mode (in NXC for example) where it could distinguish many colors, and it can also be used as a light sensor generating a 0-100 value. Therefore, there was no removal of functionality :)

The NXT 2.0 Colour Sensor can detect black, blue, green, yellow, red and white but cannot distinguish between different shades of colours (for example, different shades of green).


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What are the possible differences between LEGO elements?
I'm in a technical school in the Netherlands and we received the following questions for an assignment:

What are the other possible differences between LEGO elements?
What are the different forms of LEGO elements?
In which different colours can the LEGO elements exist?
In what packaging form can the elements be found?

Where can I find information on these various questions?

Note: this question has been translated from Dutch, feel free to check the original Dutch wording in the first revision. Also, if you have some elements of answers linking to Dutch-speaking sites, I guess that's even better... Answering in Dutch might be fine too provided there's an English translation as well.

Hallo Maxime en welkom op deze site. Helaas is de site zelf voor engelstaligen bedoeld. Ik denk dat je vraag wel interessant is voor iedereen, en daarom heb ik het vertaald, maar ik vreese dat meeste antwoorden zullen in het Engels zijn. Nog iets, ik zie dat je een student, gelieve te noteren dat je meer dan 13 moet zijn om aan de site deel te nemen (ik weet niet echt welke leeftijd de studenten van een Technasium school hebben). En, ja, eigenlijk moet je wel zo veel mogelijk in het Engels kunnen deelnemen - vraag misschien hulp aan je leraar Engels.

Cheers for the attempt at translation Joubarc - I'm not sure 1 or 2 really make sense at the moment, however I'm guessing this question is really about materials? Should 2 read "What materials are LEGO elements made from?" this would be roughly consistent with 4 which is asking about packaging materials, and often relates to colours as well...

I agree that the first two questions are a bit bizarre, but I'm confident the translation is fairly accurate. That said, being a school assignment, I trust the question may be deliberately vague in order to see what answers the students will come up with. And even as such, question 2 can certainly be answered (eg. bricks, plates, technic beams, gears, axles, wheels, whatever) - question 1 make admittedly less sense (especially the "other" which puzzles me, there may be some introductory text we're missing)

Really 4 questions in one.
To try to address question 3,

In which different colours can the LEGO elements exist?

these links to other similar questions may help:

How many different colours of LEGO bricks are there?
Is there a list of colours currently in production?


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How do I remove orange (rust?) stains from white elements?
I'm building with some yard sale Lego, and have several elements that have orange stains on them. If I had to guess, I'd say something seeped onto the bricks while they were in storage. At this point I'll probably bury them inside my MOC, but I'm curious to know if there is a method to unblemish white Lego elements?

I guess the first step would be to identify what the stuff actually is (the only idea that comes to mind being cat urine, since an unguarded box of small LEGO parts could be mistaken for a litter box by some); and then whether is comes of or not - I supposed you've tried regular cleaning options already? And are you sure it's orange spots, not simply sun-yellowed bricks?

If it's really rust stains, oxalic acid may be worth trying...

So far I tried a warm soapy water scrub with a soft toothbrush... Still have orange stains. Thankfully, there was no litter box aroma. I shy away from those yard sales. ;)

Does it happen to look anything like this?

@Ambo100 Quite simular. Sorry, I should have posted an image. I'll do that soon.

UPDATE: Buried the bricks in question while building for this weekends display. Will need to wait to disassemble MOC before a pic can be posted.

Maybe you can try with toothpaste and a toothbrush as toothpaste is one of the mildest polishers.


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Why does Lego restrict the number of colors per shape?
There are many shapes and many colors of Lego elements. Some color/shapes are rare and hard to find. Why does Lego restrict the number of colors available per shape?

The problem isn't with molding machines, but with storage.  Every distinct element (part/colour combination) has to be stored until it's no longer going to be used in production; presumably some are stored for spare parts and other ancillary uses.

The robotic warehouse has only a certain number of slots (a mere 0.5 million), so there's only so many different combinations that can be held at any one time. To make space for a new element, another needs to be retired - and retired plastic is wasted plastic.  And waste costs money, and businesses hate that.

There's another force at play here too: pretty much every set has at least one element that is unique to that set - it seems to be not so much as a business rule, as business very firm guideline. The economic implication is that if the value of the non-unique elements in a set is $10 and the set sells for $12, it doesn't mean the set is overpriced; instead, it implies the unique element has a inherent value of $2. Harmony is restored to the LEGO secondary market. This business logic can be used to explain why licensed sets are often much worse value per brick than non-licensed - each unique minifig adds over-the-odds value.  Perhaps this stretches credulity too far?
The best argument for having one unique element per set is: without a unique element, it's conceivable that someone could build this LEGO set with pieces they already own!

Few of the molds LEGO uses are running 24/7.  Swapping out molds takes about three hours, during which the molding machine (one of 64) is inactive and you have expensive European labour fussing over a machine.  Swapping colours, on the other hand, isn't such a big deal.  Stop the plastic flow, empty the mold and remove the capture box, flow the new colour for  a while until the old colour's properly flushed, then start capturing this new colour (toss all the parts molded in two colours at once into the recycling bin).
I'm hoping it's obvious why you've got to store different colours of the same part separately. I'm also hoping you can remember that LEGO makes quite a few copies of each set it sells, so that box of purple 1x4 curved slopes you see above isn't actually all that many from TLG's point of view.  They have to mold every part for a given set they're going to sell, then store them all prior to assembling them in a batch. The vast bulk of LEGO is sold around Christmas, and they don't warehouse a vast amount of the completed sets (you've seen how much air is in a box of LEGO), just enough to keep the channels flowing.  Basically, they've got to be able to store a good portion of the whole year's production, because they can - and do - assemble bricks into sets faster than they can be molded.
As an aside, this is why LUGBulk runs early in the year, when they know what they've got too much of lying around and are comfortable that there aren't going to be any production shocks.

Production planning is done well in advance. If a particular set turns out to be gangbuster-crazy popular and requires additional production (a recent example: Friends), LEGO can dip into its reserve of parts but the more unique a set (or even line) is, the less likely you are to have those parts in reserve.  This is, in fact, an argument against having unique parts - but there's only so many models you can put a bright reddish violet slide into.
As for getting the same slide in other colours... really? You want it in Pearl light gray? In reddish brown?  In tan?  Remember that LEGO is sold as sets (models), and coincidentally comprises parts in various colours; if a particular part/colour combination isn't necessary to make any of the more than a hundred models marketed in a year, you're not going to see it turn up in the secondary market.  Unique elements that turn up in expensive sets are going to be expensive, as those few Bricklink stores that do buy expensive sets for parting out aren't going to buy many of them.

Very interesting answer, I just have some doubts on the "pretty much every set has at least one element that is unique to that set" - while this may be true for licensed sets, for examples, I don't think it holds for more "mundane" ranges, especially Creator and possibly Technic. In most of the cases, uniqueness is more on the minifigs IMHO.

Do you have a reference for the fact that there are only 64 moulding machines? (References for the rest would also help covert your already excellent answer to a model one)

Simply put, because each combination of part AND colour which is currently in production means that there is one machine and one mould devoted to it, and the number of both is finite.
This may be oversimplified, but that's the gist of it. Take for example the new Friends slide which is currently produced in 'bright reddish violet'. If LEGO wanted to produce it in another colour, they have two options:

make one more mould of the part (these things aren't cheap) and devote one moulding machine to it;
stop producing it in that colour altogether, clean the mould, and start a new batch.

The second solution wouldn't cost much, but they need to be sure they won't need it in the current colour any longer. This may very well happen, but probably not before 2015.
Again, this may be simplified, but the fact is that LEGO has a finite number of elements in production (again, part and colour) because of production reasons, and they have even been trying to lower that number. So if a designer needs something in a new colour, he has to find a good justification for it.

+1 for your answer, but Josh's storage consideration angle caused me to swap my acceptance.

No problem, I must admit his answer makes much more sense than mine - storage is indeed more of a problem than moulding itself, although I'm also surprised about only 64 machines.


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What is the rarest LEGO production element (colour/shape combination)?
What is the rarest LEGO element according to the following criteria:

Genuine LEGO elements, not those available through third party vendors or otherwise modified elements. (So nothing from Brickarms.com, ChromeBricks.com, etc.)
Not prototype elements such as the Red Ghost, Yellow or Red Train Rails, etc.
The same element of a different colour counts as a different element,
(so the rarest colour/element combination)
No special production elements such as the 14k Solid Gold LEGO Employee Brick 2x4 Brick in Display Box or Gold C-3P0.
No elements that were only part of sets produced not to be sold, such as the unique Sticker for Set 4000001 which is part of set LEGO Inside Tour (LIT) Exclusive 2011 Edition - Moulding Machines or the Green BURP from the Wind Turbine - Vestas promotional set.

Agood example of "part of sets produced not to be sold" would be the green BURP, as it's only been used in that one set which was only given to Vestas employees (not that some didn't make it to the market, of course, and I've seen the green BURP in bulk actions in some rare instances). Barring that, I believe that at some point LEGOland parks did have access to more elements in alternate colours, but that probably doesn't count either since these weren't supposed to be released to the public.

@Joubarc Nice example, I have updated the question to include it. (Now I want to go and buy some Green BURPs!)

I would tend to say that any part produced for only one set would qualify, especially if said set is priced high. Looking at the inventory of 10179 Millenium Falcon UCS for example, the following candidates come to mind:

Light Bluish Gray Boat Mast Rigging Long 28 x 4
Dish 10 x 10 Inverted (Radar) with Radiating Spokes Pattern on Concave Side although it's printed so I'm not sure you're willing to accept it. I would have mentionned minifigs as well, but only Obi-Wan Kenobi (Old, Light Flesh) is exclusive to the set and its individual parts are used in other sets.

Considering the price the set goes for nowadays, and the fact that most people who buy it will probably build it once and leave it so (that is, if they open the box at all), I think the grey boat mast rigging is a very good candidate. There are four people selling some on BrickLink as of february 2013, but a glance at the prices asked comforts me in my reasoning. Even the printed radar dish is cheaper.

Agreed, I think the mast rigging is a good candidate. I think printed elements are acceptable but since both the radar and the mast rigging are both from the same set, I suppose it doesn't make any difference. Interesting point on the minifig - I would say that since it is made up of parts, then I would say the minifig as a whole doesn't count even though it is only used in that one set.

I'm not sure whether to consider these real Lego parts or not, but many of the old HO scale vehicles and greenery are incredibly rare. For example, the Jaguar is quite rare in any color, but especially in red and black.

@jncranton I never thought of the old HO scale vehicles. I suppose we should also consider the Pull-Along Duck from 1935, there can't be many of those still around.

+1 for this - although I feel the question is a bit vague in this respect in that @mcqwerty didn't actually specify what "element" meant ;)

712pb01 Plate, Round Curved 4 x 8 Left with Red Line on Curved Edge Pattern
To be honest, I don't know if this is especially rare. I do know, however, that to find the rarest part we'll need to factor in:
1. Parts that appear in small numbers in very few sets
For example:

"White Minifig, Headgear Hair Female Pigtails" piece only appeared in a few sets.
The parts unique to the 10179 Millennium Falcon UCS.

Often, rare parts have an unusual design or colour.
2. Of those, sets that had a limited production run
Sets with a limited run might include:

Promotional sets (although these rarely have unique parts)
Sets that are limited to a single locality

The Millennium Falcon might be a candidate here.
3. Of those, parts that are unlikely to have survived the ravages of time
This might include:

Old sets - anything from the 1950s, for example
Sets designed for community play, e.g. Educational establishments

All things considered, I imagine that the rarest piece of proper LEGO is from one of the oldest sets: which is why I suggest something like, "712pb01 Plate, Round Curved 4 x 8 Left with Red Line on Curved Edge Pattern" that appeared in a single set in 1958.
Alternatively, (if you care to count them as part of the system) many of the parts from the 1940s Automatic Binding Bricks era will be quite rare by now.

How could I forget about the white minifig female hair... (although in all fairness I've seen some sold at auctions a few years ago, and these were even provided by LEGO itself)

I was just reading about the 8485 Technic Control Center II, where you can make a dinosaur, helicopter, or hovercraft controlled by a big panel, and which I have on hand. According to a reviewer (http://www.eurobricks.com/forum/index.php?showtopic=75864) there are a few rare pieces that were included with this set, which retailed for $219 in 1995. The price of the set and quickly-outdated electronics probably could imply that the set is relatively rare. Some of the parts are pictured here - http://www.flickr.com/photos/mostlytechnic/8158411568/
Red wing plates (x2 Left, x2 Right) that were used in the helicopter build, and one other set.
Little white coils for bundling wires together, only used in an earlier Multi Control set and educational sets (probably quickly lost).
And a black steering yoke used in the dinosaur build - only ever included in this set. It was released in white in a 1980s car set.
This might be one of the rarest individual parts that's not from a promotional or movie-themed set.

None of these seem to fetch too high a price - admittedly, that's not necessarily an indication of their rarity, but since the demand isn't particularly high it's still possible to get some relatively easily. Good find, though - and welcome to bricks.se!

Based on the conversation in this thread, the 2x4 brick in trans-neon-green is also quite rare. Last selling price on Bricklink was from Oct 2014 and was set to $75.

As that part was never in any set (the linked thread says so), it probably is a prototype element or something and thus fails some of the OP's criteria.

Perhaps the Chrome Green Rock 1 x 1 Crystal 5 Point?
It is the only chrome green part.

How about a surprisingly rare part: the Lime Green 1x1 plate. Only produced in one set in 2005.
Edit: Re-issued in 2014,so for 9 years, it was rare.

Oh? Bricklink says it was in three sets.
granted, one of those sets is a monthly mini model build.
OTOH, Bricklink says 6 different colors of 1x1 plate came in only one set each. Of those, the Maersk blue only had two in a set from 1980.

I didn't realize they re-released it! Brickset still lists it as only coming in the one set from 10 years ago, and when I went looking to buy some last year, they were $1+ each on Bricklink.
Anyway, I think a much more interesting answer to this question than a rare one-off piece for a licensed set is a common color and common part that in combination are rare.

At this point, I'd be interested to see what mcqwerty has to say, what with all this new activity and STILL without a chosen answer.

@gev I am here, watching and enjoying the conversation. I'm not sure there is a 'correct' answer since it depends on even more factors than listed in my original question.

It's impossible to provide an accurate answer without accurate information to base it off of.  Without knowing production quantities on every set, it is impossible to know if there's a part that only comes one per copy of a set that sold 10 million units, or if there's another part that only comes ten copies of a set that sold 10,000 units.  Age of sets can also affect the answer because parts that have not been made in decades will exist in much smaller numbers now than when they were brand-new, due to all the various ways that a LEGO part could be destroyed over the years.  Some sets have been recalled and changed, which may have allowed a small number of a rare element to make it out into the wild, after which the supply was cut off.  And some elements have been retired almost immediately after they were first put into production.  Assuming stuff like SDCC minifigs are excluded (not meant to be sold), I have to put my vote on 8-spoked wheel #51377.  In 2005, they first introduced this wheel in metallic-silver for a Designer set and a Tiny Turbos set.  In 2006, they produced it in pearl-gold for the first Batmobile and the Catwoman/Dragster set.  Before those two Batman sets went out of production, they had introduced the reversible wheel #55981 with six spokes on one side and bolts on the other.  In the two Batman sets, they replaced the 8-spoke wheel with the new reversible one, which means they made the 8-spoke wheel in pearl-gold for only a few months before the mold was permanently retired.  I bought one copy of each Batman set at release, and a second copy soon after, and only got the 8-spoke wheel in the first copies I bought.  And that's too bad, because it's a really cool looking wheel.

Antannae piece from the 70s. The ones nowadays are almost all broken, so these are rare. Also Chrome Gold 2x2


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Can you keep blocks clutched together in big chunks? Will blocks loose their "clutch power" after years of that kind of keeping?
I keep my blocks of same type in big assembled chunks, for easy building and finding bricks, but I am worried, is it safe for them or will they tend to lose strength in some time (years maybe)?

How did I miss that duplicate?! Sorry.