This site offers an excellent analysis, complete with charts, on how voter turnout compared to 2004 and 2000.
Particularly:

• McCain did better among the rich than the poor, but his lead decreased among the highest income brackets.
• No massive youth turnout, again. Instead, Obama got a much larger share of the youth vote.
• As in 2004 and 2000, the map was very partisan by state (see the charts for more details).