Alas, I have never had the chance to read the books, but I have seen the Lord of the Rings trilogy and just saw "The Hobbit" a few days ago. The movie was okay, though I really wished it had been treated more seriously, like in The Lord of the Rings. I didn't care much for the childish humor and very poor physics, but from what I've heard, it stuck very close to the book. It even filled in parts of the book that were missing, which is very rare. Usually it's the other way around.
I plan to read the books some day. I have learned to watch the movies first and read the books later, because usually if you read the books first, the movies only disappoint. I'm looking forward to seeing what they do with the next two "Hobbits" films, though.
Matt
P.S. I just received the Lord of the Rings trilogy (set) for today's Christmas celebration with my immediate family. I'm planning on watching all three of them on New Year's Eve (In my family it was a tradition to watch a marathon of films leading up until midnight. I plan to carry on that tradition).