If Obama could pull through Rev. Wright, he can pull through this
99% of politicians would've collapsed after a disaster like Rev. Wright. That whole fiasco struck at the core of Obama's fundamental vulnerability, which was that he was black and potentially scary to white voters. But Obama pulled through, and compared to that, this one debate performance — in which he didn't say anything self-incriminating or damaging, mind you — is well within his abilities to fight back from.
The voters are just waiting to see a determined, principled, and confident Obama in the next debate. Biden, as amazing as he was last night, is not the president and can't be a stand-in for him. Biden's job was to stop the bleeding and take the mojo out of the Romney Resurgence narrative. He did both very well.
Now, it's Obama's turn, and I'm certain that he will deliver. As we all expected, it will be a close election, but Obama's done too much good for the country, and he's too well-liked by the population to be fatally wounded by just one anemic debate performance.
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I noticed several times during 2008 that Obama was able to come back when the chips were down.
I was in the Hillary camp during the 2008 primaries, and each time after we beat him, he would come back. 
And yes, he was able to weather the Rev. Wright scandal, the Palin bounce, etc. and a lot of other things people said would be damaging.
So while I think some people are being too naive in expecting Obama to jump up 10 points next week, I think on the other side of the ledger you are certainly right that Obama has a history of being underestimated.
He just needs to come through one last time. If he can do that, he can win a 2nd Term. 
