I generally do not watch the movie of a book I have read. Like wise I will not read a book after seeing the movie.

When I read a book I create mental images of the people and places. If I watch a movie I'm forced to see X actor as that person or X set as the location. And while they might do a good job, it is not what I created in my mind. It tends to have deviated from the book. Books often spend great amounts of type descriping a persons thoughts, feelings and fears, a movie can not do that.