disappointed reading

Do you ever give up on a book part way through?

I'm struggling right now with the current book I'm reading. I've made it to about the halfway point and I just don't care enough to really see how it ends. I'm quite disappointed in the book, actually. It was misleading: the synopsis on the back suggested that the plot revolved around time travel and detective work and in reality it seems to be about trickery and the human desire to believe things that aren't real.

The plot has followed two major arcs so far, both about different characters being tricked into believing that they have traveled through time, with the omniscient narrator revealing the trickery afterwards. And I just don't care. It's not poorly written, it's just I would have never picked up the book if the brief had given me a more accurate description. It's a pet peeve of mine when the synopsis is misleading; I rely on those to help choose books based on my interests, and the actual content of this book is nothing to do with what I was told it would be about.

Part of me wants to keep reading, to see if maybe, just maybe come part three there might be some real time travel and wonder to discover. Plus I paid about ten dollars for the thing and I feel a little obligated to see it through based on that. Neither of which strike me as particularly compelling reasons to keep reading, really. Plus I have more interesting books around just waiting for my attention.

I've been reading this for over two weeks now and can barely bring myself to pick the darn thing up during my lunch hour at work, when I typically do a large chunk of my reading. I kind of want to power through it, because there isn't that much left but honestly the idea is a little dreadful.

How do you decide whether it's time to give up on a book?