According to John Nack of Adobe, Photoshop CS3 Beta will be available on Adobe Labs today or tomorrow. Of course the best feature is native Mac Intel support, but I'm sure there are some other great features to check out. A great deal of those are listed in an article on Macworld's website:
John's full post is available at the link below, and includes an FAQ and links to more info.
Also, check out this great blog post from another Adobe employee, Scott Byer.