Katie Holmes isn't going to be in it at all.
http://movies.ign.com/objects/752/752133.html
I've been anxiously awaiting this movie ever since seeing Batman Begins, which is by far the best comic book movie ever made. It was awesome.
I was originally pretty pissed to find out Ledger would be playing the Joker, but from the trailer... he seems to do a damn good job.
I still think they should have cast Steve Buscemi, as originally rumored. He would have been perfect.