Dunno if this has been diaried, but I just got a copy of Zogby's September newsletter:
http://www.zogby.com/Sept-ZRA.pdf
In it, he claims that while a lot of voters (including a majority of independents) saw the ads, most of them didn't believe the SBVs' stories. The ad campaign ended up shoring up the Democrat base and pissing off the electorate, raising turnout motivation.
A crucial excerpt:
The bad news for Mr. Bush is that the Law of Unintended Consequences seems to be taking hold. While 13% of the electorate has moved away from Mr. Kerry because of the ads, 23% has moved away from Mr. Bush because of the ads. And while one-fifth of the electorate believes the Swift Boat Veterans' side of the story, fully half (50%) believe the story of Mr. Kerry and his fellow crewmates. Mr. Bush's campaign may be hurt on two fronts by these ads, first from the independent swing vote, and second by the Democratic base. One in five (20%) independent voters have moved away from Mr. Bush in response to the ads, while only 13% have moved away from Mr. Kerry. Independents also remain unconvinced of the charges--while 16% believe the Swift Boat Veterans, nearly half (49%) believe Mr. Kerry's side of the story.
Zogby then goes on to claim that even Republicans had a hard time believing the Swifties' claims. Why, then, did Bush rise in the polls during August? A better presence in the media. No specifics are given to back that up, but the central point here is that the smear campaign didn't work. So much for the evil genius of Karl Rove.