One last thought on the "how screwed" theme, in favor the "not screwed" position: Suppose we assume--plausibly, I think--that Jeremiah Wright would be as damaging to Obama in the general as getting swift-boated was to John Kerry. It's worth keeping in mind that Kerry lost by less than three percent of the popular vote at a time when the war and the economy weren't looking nearly as problematic as they are today. And that Kerry isn't nearly as talented a politician as Obama. So it's not like this thing wouldn't be winnable.
Obviously that changes if Wright turns out to be significantly more damaging than Kerry's swift-boating... But the basic point is that a lot of the commenters are right: Obama (and Clinton for that matter), would still have a lot going for them in the general.