This is probably true, but I think it's more a concern for them in 2012 -- nothing dramatically good is going to happen with the economy between now and November. Even if it comes back gangbusters, employment is always lagging. Also, bad situations are inherently more energizing and they have a wider "spread" -- even if Jack gets his job back, if his wife Jill is still unemployed he'll still be angry -- in 75% of the possible outcomes among those two, they'll feel like times are still bad.
The incumbent is always on the business end of this; so if I am the opposition, I want to pick candidates who can plausibly vamp as "outsiders," even if it's a total snow job.
I think the most likely outcome is the GOP picks up a ton (40+) of House seats this fall even with borderline crazy / incompetent nominees, but then all those pick-ups are extremely vulnerable for 2012. If the economy is stillborn it's a horse race, while if it has recovered Obama has a Reagan-like re-election cakewalk and most if not all of those first-termers drown in the higher turnout wave. Remember also that the GOP as currently configured* is demographically doomed outside the confederacy; as time elapses it tweaks the electorate that much more in favor of the Dems while, given age and gender composition differences, the GOP is gouged relatively more by literal die-off.
(* Obviously this must and will change, as the GOP re-centers itself.)