Democrats are at a ceiling, we hold basically all of the competitive seats. The question is not if Democrats will lose seats, it is how many, and whether it is enough to lose the majority. At this point, it is just too early to make any meaningful predictions.
http://www.fivethirtyeight.com/2010/04/generic-ballot-points-toward-possible.html">Nate Silver thinks that a 20 seat loss would be among the best possible outcomes, but also sees a possible nightmare scenario where Democrats lose 80 seats. I think this is a pretty reasonable analysis.
The special election for Murtha's seat in a few weeks could be a harbinger of things to come, and I don't really expect Critz to win.