I honestly don't know what to say about this. I thought it was just a rumor up until a couple of days ago, and now that it's actually happened, I'm not sure how things in the graphics industry are going to change (or even if they will change). Here's the official press release.
Updates! By Steve McBarnes
Jon Carvill interview at DriverHeaven.
ATI/AMD slideshow and answers to reader questions at [H]ard|OCP.