William Gibson thinks OBL would prefer to see Bush re-elected and that his new tape was a clever attempt at helping that happen:

I wouldn’t go so far as to suggest that OBL fears Kerry any more than Bush. But Kerry can only comprise an unknown, and why allow the other team to introduce an unknown when your familiar power-symbiote has always proven so wonderously adept at doing everything you’d most want him to do?

OBL today is probably a very satisfied, very optimistic man, and if he can skew the last-minute dynamic of the election in Bush’s favor, he’ll have cause to be all the more satisfied.