I find it pretty easy to consider the movie and the book two different, unrelated entities, which is good for me because it means I don't get all hung up on the movie being "wrong" or missing things out. They're two vastly different forms of media and it would be impossible to fit all the information from a single book into a single movie... and I don't think it's a bad thing that it's happening so often, either, because it's always nice for me to see how other people envisioned the books I've read.