In PA she cost McCain whatever cred he had. He got whupped like 65-45 in PA. I assume that she had a similar effect in other rustbelt and borderline states.
Does seem like Palin had more of an impact on the election results than VP candidates normally do - and in a bad way.
According to the exit polls, just 38% of voters thought Sarah Palin was "qualified to be president should it become necessary". 66% thought Joe Biden was.
Half of all voters (49%) thought Joe Biden was qualified - and Sarah Palin was not; and those went for Obama by 91% to 8%. In comparison, just one in five voters thought Palin was qualified and Biden was not.
There's a bit of a chicken/egg thing going on here - did they go for Obama because they didnt trust Palin or did they not trust Palin because they were Obama voters? But either way, those who saw a difference between the two VP candidates overwhelmingly thought better of Biden, and those who did so overwhelmingly voted for Obama/Biden.
Basically, if a full half of all voters think your VP candidate is unqualified, you have a problem.