Used to be, I had this neurotic compulsion to finish every book I started, no matter how much I hated it. And recently I asked myself, why am I torturing myself? There are way too many good books out there to waste my time on something I don't like. So now I give it 50 pages and if I'm not enjoying it by then, then bye bye book.
So I just gave up on Black Silk by Judith Ivory (it's a Romance). I was hating the characters and the plot didn't seem to be going anywhere interesting. So I pitched it. Luckily I got it from the library, so I don't have to feel angry about wasting any money.