There's a school of thought out there in the political realm that, given the nature of the economy and the fact that Democrats control everything, Republicans are to make huge gains in the fall. The out-party almost always makes gains in off years, and incumbents do badly when the economy does badly. These are pretty hard and fast rules of political science.
However, some are starting to notice the potential for mitigating factors, that may cushion the coming GOP blow. Namely, that the Tea party has driven the GOP to the hard, hard right. Jon Chait, notes that in at least 4 Senate races, tea party right has made things easier for Democrats with their nuttiness. The most famous example being Harry Reid, who looked to be in real trouble till the tea party handed him an opponent that is completely nuts.
Here's Kevin Drum noting that the D's are picking up ground with independent voters. Could they be turned off by the tea party? Stay tuned.