The Ultimate Editions are definitely worth getting. The extras are so interesting..all sorts of things on the making of the movies. Including interviews from when the first movies were being filmed. There have been little interview bits with Daniel, Rupert, and Emma done during the filming of all the movies through six...least from what I've seen so far. I still have to watch the extra goodies on 3 and 4 that I just got.
Every set has a little book with all sorts of pictures from the making of the movie.
Oh...I also just got this book. Harry Potter Film Wizardry. All sorts of information about the making of the movies. And there are replicas of some of the props. Like the letter that Harry gets about being accepted to Hogwarts..the Marauder's Map...a flyer for Fred and George's store...the cover of the Advanced Potion book. I love it.
And no one else is ever getting their mits on it.
I'm a bit protective of my Potter paraphernalia.
But I know I'd be pissed if any of those replica things got damaged. So I'm not sharing.
Harry Potter Film Wizardry