Rasmussen has a new poll out showing that people are leaving both the democrat and republican party at a pretty steady rate. Some would argue that this is because of voter frustration with both parties and a desire for a change of course in the way we do politics.
I'm not so sure. I think that while both parties have had a decrease in numbers, the republicans have a better footing over-all. For example, if you ask most tea-party members where they stand politically, you are more likely to here them call themselves "conservative" rather than republican. While they may not identify with Republicans out-right they are still fired up and ready to go to the polls and vote that way. Democrats on the other hand are becoming despondent about their chances in November. Plus many on that side are feeling betrayed by the party leadership and how they haven't delivered on the nebulous "change" promise.
Also there's the deflation of the cult of personality that Obama created during the '08 campaign. It's difficult to translate the energy he generated into sustainable interest over the long term, especially when you have to act more "presidential".
I've been a little back and forth as to how the election will turn out but I feel (a little more now after that poll) that things are still pointing to a big year for Republicans...even if these that vote for them don't actually call themselves that.