How does Chesscube.com rating compare to USCF and FIDE ratings? My Chesscube is 1800. I would like to have the strength of 2100 or 1900 USCF and FIDE. What Chesscube rating do I need?
There is no way to directly compare ratings from distinct populations. 

However, it's not true that online chess and OTB populations are really distinct. There are players who have ratings in both OTB and online chess.

So, you can compare your rating this way: Find players in Chesscube who has also OTB ratings, select two of them, both have ratings close to your rating, one of them is higher than you, one of them is lower than you.

Your expected rating is between their OTB rating. If you pick more player from Chesscube, and pick more closer players, you will get smaller interval, thus more accurate estimate.

Example: 

            Online    |    OTB
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Player A     1750     |    1630
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Player B     1850     |    1730
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You          1800     | Expected: ~1680, Probably between 1630-1730
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