If there was anything in Obama's past that would seriously jeopardize his candidacy, it would have come out by now. Hillary and Obama voted the same way on pretty much everything, making the primary race about character and judgement. Seeing as how badly Hillary wanted the presidency, if there was anything out there, she would have dragged it out and brought him down.
Obama's been veted for nearly 2 years now. There's nothing to see. The republicans are already trying to cut their loses from McCain and are focusing on their senate races. I'm sorry, but McCain's done, and there isn't any "character/judgement fault" of Obama's that's going to change that.