I read an article somewhere that Obama's very sophisticated polling operation showed no such bounce unlike the buzz out there that it did.
IIRC the bounce was merely anti-Obama voters who were unsure about Romney.
I don't think that was all of it. IIRC, Obama lost some points in the polls as well as Romney picking up some ground. Kind of what was mentioned earlier of voters who were down on Romney as the lesser of two evils who first got a chance to see him beyond sound bites or attack ads in the role of Moderate Romney
tm.