Here are the the last 60 years' worth of midterm losses, going back to the second Truman midterm, according to Wikipedia for election-on-election losses, which is the standard I use all around. For 2010 I'm using the current CNN projection of a 65 seat Republican gain and a 243 R - 192 D House. Click for full size goodness.

Midterm Losses

Congratulations, Mister President.