Its mostly little things like Gandalf and his powers, stuff that isn't even explained very clearly in the books (like the fact that Gandalf isn;'t human, but rather a demi-god who has assumed human form). But for the most part I agree, it certainly won;'t impair someones ability to enjoy the films if they haven;t read the books. However if you see the movies first the books must seem pretty slow and boring by comparison.
