Somebody: Sure, but we already know that mid-term elections normally have much lower turnouts than Presidential elections. This last election was perfectly in line with the historical precedent in this regard. Comparing 2010 to 2008 is comparing apples and oranges. The relevant comparison is 2010 to 2006, 2002, 1998, etc. And again, the turnout this time looks like it was higher than in those mid-terms.
We're left then with the composition of the electorate, of core Democratic versus core Republican turnout, as you and Doug point out. However, so far I see no data that the youth or minority turnout was lower than is typical for mid-term elections. I'd be happy to be proved wrong.