I do tend to prefer non-movie covers but I'm not totally against it. I do have the Slumdog Millionaire one and my cover of Boy A is from the TV adaptation (but I quite like that cover).
I think my main reason for avoiding them is the representation factor. Similar to if I watch a movie before I read the book, then I imagine the characters/locations/etc as shown in the movie, and I prefer to create and imagine them myself from the descriptions. When a book has the actors on the front, then I tend to imagine the characters as the actors, as I tend to look at the front cover quite a lot.
Also, I always think the book is seperate from the movie. A movie is merely an adaptation, it'll never be an exact replica, it could never be. So, the book should look different and remain with it's original cover.
PLUS, they're usually a lot better. E.g. The Reader.
Just think..they'll release a New Moon one with Jacob on the cover.