It doesn't happen often. In fact, never before.
I like books and I like movies but I usually don't like when one becomes the other. And I'll tell you why. The very nature of books, printed words, all the thoughts and feelings being laid out, the imagery taking place in the mind of the reader, is altered when put on a screen - big or small - and some of what I may or may not have thought is lost.
This is not to say there are not some really well done book to movie adaptations. True to the spirit of the story without being too literal and those I can respect. (The Hunger Games anyone, anyone?)
But it's very rare when I find a movie that I like BETTER than the book from which it was adapted.
And The Devil Wears Prada is that one exception. I just finished reading the book and I have to say, I don't like it nearly as much as the movie. This is not because I saw the movie first, I've done that before (The Firm and The Lord of the Rings trilogy - don't shoot, I know, it's a classic.) and even with the imagery preset in my mind, the books were much more thorough and well done.
In the case of The Devil Wears Prada, the book, I didn't like the main character, which makes it hard to enjoy, because I'm pretty sure we're supposed to sympathize with her. She's a chain smoker, which might not matter to others but I don't like it in a person and she doesn't have the integrity they give to Anne Hathaway's version in the movie. Also, the evil boss is not so evil in the book, just demanding and mean. She never asks the impossible, as is suggested in the movie, just to her exacting specifications. Andy's boyfriend in the movie is a nice well-adjusted guy, in the book he's a holier-than-thou, weak, little man. Nigel, played by Stanley Tucci - who I LOVE - in the movie is actually an amalgamation of three characters from the book and the impact of his influence on Andy is diluted. The only character that carried over faithfully from print to film was the first assistant, Emily, and that was okay because I liked her. In both places.
There are other differences, obviously, but the it's mainly that Andy is not a nice or good person in the book and her lack of principles makes it had to be on her side.
So score a few zillion for the written word and one for the big screen.
This is me and that's what I thought.