I think this question deserves it's own thread.

Personally, I read the book before watching the movie, or read the book and never watch the movie, or watch the movie but never read the book, but what I don't like is reading the book after watchig the movie. Usually when I read a book it feels like the things are happening to me, but when I watch a movie I feels like the things are happening to someone else and I'm just there on the sideline. When reading the book after watching the movie I can't get into it the way I'm used to.

But I've seen many people say that when they read a book it also feels like they're watching a movie, and in that case I think the order wouldn't matter.