I'm a bit annoyed at this. I already have my own personal idea of who the characters are and their stories and would rather a lot of the missin' pieces remain missing. I think this is one series that cannot be translated into film without it mitgatin' it in the process.
NO SPOILERS PLEASE IN THIS THREAD - some of us haven't finished reading the books yet!

Snake kills Dumbledore.
I don't see this as a good thing, personally. The books are meant to be an imaginative product, with people using their imaginations to fill gaps. Filming them will force them into a straitjacket and turn them into yet another fantasy miniseries. Not only that, but people who aren't Constant King Readers will not understand all the connections between his works, so they'll likely be dumbed out for more shooting scenes.
Then again, if I'd trust any company with the franchise, it'd be HBO.
This. The series itself spans over 3000 pages; a lot of stuff will have to be cut out. The animation would also be a nightmare because of all the magic and post-apocalyptic scenery would either force a Lord of the Rings size budget or be sloppy.