It took me a long time to realize that you don't have to finish a book if you are not enjoying it.
POD! I have some friends who feel like they MUST finish a book if they start it. Some even feel like they MUST finish the whole series, if they start the first book. Or maybe they don't actually waste their time reading an entire series they don't like, but they feel bad about not doing it. My feeling is, there are so many awesome books in the world, it's probably physically impossible for me to read all the ones I'm interested in within my lifetime, so why would I force myself to continue reading something I didn't care for? That's also why I don't often reread books... just not enough time. I find it so liberating to say, "I don't like this book. I don't look forward to reading it. I'm not going to read it anymore."
Currently on my pile of books I've started, but not touched for a long time, which are in danger of being discarded entirely (along with the peeves they inspire):
--The White Queen, by Philippa Gregory. I really want to read the whole series and normally I like historical royal romance. I've read several of her other books (the Boleyn ones) and found them enjoyably trashy. But nothing much seems to be happening here, yet I have the feeling that horrible things will
--National Geographic travel guide to Hong Kong: I read their travel guide to Hawaii and it was quite well-written and evocative. This is much more dry (which I suppose you might expect from a travel guide) and really turned me off by stating on the first page that people in Hong Kong are unpleasant and unfriendly.
--Roma, by Steven Saylor. Great books for learning more about ancient Roman history and development. But in every single chapter all the likable characters get beaten, raped, tortured, exiled, and/or murdered. It's depressing.