What is the smallest result you publish on ArXiv? In essence, the question is:

What is the least publishable unit for the ArXiv?

Of particular interest are fields that use the ArXiv extensively such as quantum computing. But comments on other fields and preprint services (like, ECCC &amp; ePrint) are also welcome.

Detailed question
This is based on the following two questions:

When should you say what you know?
How do you decide when you have enough research results to write a paper and to which journal you submit the paper

In particular, on Jukka Suomela's comment on this answer:

I think ArXiving your results ASAP is a good idea. Please keep in mind that an ArXiv manuscript does not need to constitute a minimum publishable unit. I think it is perfectly ok to submit a 2-page proof to ArXiv, even though it would be obviously too short as a conference or journal paper. Resolving an open problem that other people would like to solve is more than enough.

In my field (quantum computing) it seems that every preprint I see on the ArXiv is a publication-level paper, released early so that we don't have to wait for conference proceedings or journal turnaround. It is intimidating to submit something that is not at publication-level. Is it alright to put up results which are partial or only slight extensions of existing work? Is it alright to put up results that are potentially interesting (i.e. you've given some talks on them and not everybody fell asleep) but you doubt would get into a top-conference or journal? Do you have advice on when to share results on ArXiv or similar preprint-servers? Can sharing results early hurt you?

Some specific background
Just to make the question more personal, I'll include a further motivation. However, I am hoping to receive answers that give more general guidelines that I (and others) could follow in the future.
I did some work on unitary t-designs in which I extended an existing theorem (in a way that is kind of useful, but the proof of the original just needs to be modified slightly -- so no new idea; i.e. when I talked to the author of the earlier paper his comment was along the lines of &quot;oh cool, didn't think about that&quot;, and for the proof I had to say about a sentence and then he was like &quot;okay, I see how you would prove that&quot;), proved some easy results, and provided an alternative proof of a lower bound.
I wrote up a pretty verbose paper that I keep on my website, but unfortunately I am not well read enough in the field to really understand how it fits in the bigger picture (and I think that is the biggest weak-point, that I doubt I could overcome easily). I keep the text around mostly as a sort of &quot;I worked on this&quot; note and since I give talks on the topic sometimes. It has also come in useful once to a friend since I make a pretty gentle intro and so he used it as a basic starting point to relate some of his work to designs (although he didn't use any of the results in the paper, just like a lecture note on definitions).
Would this be an example of something that I should put up on the ArXiv? or is the appropriate measure to keep it in on my website?
ArXiv papers still need to be recognizable as papers. I'd only put something on the arXiv if I'd feel comfortable publishing it as a letter in a journal (like, say, Information Processing Letters). For stuff that's even smaller than that, but that I still want to put on some sort of public record, I'll just make a blog post.

But in your case, if you've written it up as a preprint anyway, and you clearly state in it how much or how little is new, then why not? ArXiv papers don't actually have to have any new research content — survey papers are also welcome — so a paper that's mostly a survey but that extends the problem a small step in some direction doesn't sound problematic to me.