Actually I'm going to go to bed soon, as it's 1 AM here.
There's been a lot of good, insightful commentary about the whole PUMA voters (HRC supporters who are going to vote for McCain over Obama) and how it's largely a media creation. I think this is true - sure, there's some Clintonites for McCain (who were brilliantly humiliated by Chris Matthews today) but I don't think they're going to make a significant impact.
However, disaffected Republicans voting for Bob Barr are probably going to have much more of an impact on McCain's chances - though few polls even ask about Nader or Barr, those that do show Barr grabbing at least 3% of McCain's vote. This story doesn't get kicked around as much - though maybe it will next week in Minneapolis - since it's not as sexy, and also cause it would draw attention to a third party.
I'd find some actual links to the polls but I'm too tired. Go read a real blog if you want decent research!