I'm the same way sometimes. It just depends on how interesting I find the movie. Take in point I just finished Chocolat the book after watching the movie like...jeez a year ago maybe? It just sat and sat, I think because I already knew the outcome. It wasn't really a surprise. The story was okay but nothing spectacular.
I can't toss movies from books because thats how I sometimes find an excellent read. I think its more or less how I respond to the characters and the premise. It has to be worth it either way for me to do both.

