It's been known for a while now, but I wanted to post it here nevertheless.
"BURBANK, CA, MARCH 12, 2008 - Warner Bros. Pictures today announced that the screen adaptation of J.K. Rowling's final book in the series, Harry Potter and the Deathly Hallows, will be released in two parts. The announcement was made by Jeff Robinov, President of Warner Bros. Pictures Group." [read more]
I think its a good decision. The book has constant action and it would be very difficult to cut parts without affecting the events line. Also good for Warner Brothers of course but I'm sure the fans are happy with the idea.