I'm not that worried about an attack actually (inside the US). I think there is more of a political attack - AQ needs to get Kerry into office to get out from under and regroup - this is their gambit here.
This isn't gonna do jack for Kerry. Just the opposite. Which is why I think AQ just gave up on their candidate and had decided to try a desperation attack.
Just heard on Fox that the tape has been authenticated by the U.S. How does this cut? Kerry will surely use it to hammer the Tora Bora "Bush let him get away" theme. But anything that focuses the public on the direct terrorist threat has to help Bush on some level.