Obama has the momentum now, no doubt about it. But what strikes me is that it was McCain's own ill-advised post convention tactics that allowed Obama to get his mojo back.
McCain made a few drastic moves that boosted him in the short term, but is working against him at this point.
Let's think about how McCain handled his campaign thus far, post-convention. He's made some very assertive moves that increased his post-convention bounce, but they're all falling flat now.
First, he forfeited his experience theme in favor of the politically-motivated theme of change. When you think of this in terms of marketing, McCain has tried to shift his brand in mid-campaign. Not only is this confusing to John Q. Public, but it both establishes the fact that Obama had it right all along, and that Obama is the leader while McCain is the follower. Plus, it doesn't pass the BS test: who's more likely to change Washington: a 3 decade long insider or Obama.
2nd "bold" McCain decision: go for blood against Obama, and do it with lies and deceit. Obama handled the situation fairly well, I think. He defended himself without whining about unfair treatment in the media, which was certainly a temptation, and he allowed others to criticize McCain's tactics. Then it reached a critical mass and McCain was seen (in the media and even by Repubs) as resorting to vicious lies.
This has allowed Obama to take his gloves off against McCain. Before, the media would have said, "Mr. Obama used to be about hope, now he's a typical politician." But who can now blame Obama for going on the offensive? You can only take so many punches before you're forced to fight back. Also, all the stories about McCain's lies and viciousness have forced McCain to back off for a bit. Obama now has a window of opportunity to work with.
Finally, the ultimate short-term boost -- Palin. Her star is fading fast: her extreme views are coming to light, her lack of substance can no longer be seen as political or media spin, and the investigations against her aren't helping either. Palin is now seen as a political choice, one who might help McCain get elected as opposed to actually helping McCain govern. Who's putting politics ahead of country again? How can McCain still make that claim?
Bottom line: if McCain had made some of these moves in the 2 weeks prior to the election, his short-term vision may have paid off. As it stands, McCain can only blame himself (and his own admitted ignorance of the economy) for Obama's recent surge in the polls.