I think John Dickerson basically nails it over at Slate. Obama basically proved he could dance last night and held his own with Clinton over policy. I think the following point is particularly intersting:
In the end, the attack on Obama as a substance-free orator may backfire. It lowers the bar for him, so that when he offers detailed plans and speaks of his accomplishments, he sounds commanding. The attack also gives him an opening to take umbrage on behalf of his supporters, one of the easiest and effective political postures to take. Obama flamboyantly exploited this opportunity. Noting that Clinton lately had been urging voters to turn from him by saying, "Let's get real," Obama said, "The implication is that the people who've been voting for me or are involved in my campaign are somehow delusional."
I remember this happening to Al Gore in his run at Bush. Basically everyone said Gore was this incredible debater, thus all Bush had to do was look not-stupid and he wins. Obama is superior to Bush, but Dickerson is right. Her own campaign basically lowered the bar for Barack and he exploited the opening.