I think Barack Obama's decision to resign from Trinity United Church of Christ must ultimately be regarded as a decision in risk management. You take a little bit of a hit now -- and really, it hasn't been much of one, because there are a million competing stories in the news cycle right now -- and probably concede a talking point or two to your detractors for the rest of the election ("he seemed just fine with that stuff for the first 20 years").
But you reduce the risk -- or at least the resonance -- of someone else saying something stupid at just the wrong time. You can clearly make out the two points in the Gallup daily tracking poll where the Reverend Wright stuff was dominating the news. Obama recovery from those moments was fairly rapid and fairly robust.* But the general election, unlike the primaries, is a one-and-done. If you have one of those 10-day slumps in your polling numbers and it coincides with Election Day ... hello, President McCain.
My sense, by the way, is that if this election breaks, it'll tend to break early for Obama or late for McCain.
* Which is not to say that there wasn't any permanent damage. Clearly in my opinion he lost some general election votes for good, though I suspect those are the sorts of votes that he might have eventually lost anyway.