I always finished every book I started. A few years ago I joined a book club in which most of the members are old enough to be my mother or grandmother. One of them has a 50 page rule. If she can't get into a book she stops reading. She'll just say, "I'm too close to death to waste my time reading crap!" then talk about how bad/bored/etc the 1st 50 pages were. I think that's a great and liberating idea.