I much prefer reading a book to the films especially Harry Potter for example but that might just be me................I've read Twilight and recently read New Moon and although I've seen Twilight I've no interest in the other as the film (I have debates with my daughter about this lol)!
I read P.S. I love you and loved it...bought the film in Asda for about £5 watched half and hour then switched it off.
Think it depends on how good the film is, how much it sticks to the book and the individual.