I think most people (in Pennsylvania anyway), have switched their party affiliation strictly because they want to vote for Obama. They aren't going to switch back to McCain in the general, or they wouldn't have bothered switching in the first place.

Its been drilled into us for months now, how Hillary has a "double digit lead in Pa." and I think that was the big impetus and the only one for changing party affiliation. People don't go to that kind of trouble if their candidate of choice appears to be a lock, as Hillary supposedly was here.