Name switches. Several times in books I'll be in a middle of a scene, and suddenly a sentence will make absolutely no sense, and you have to pull yourself out of the scene for a minute to figure out what's really going on--and that the problem is that the author put the name of the wrong character down. And it's usually fairly obvious, too--I mean, I've seen it where the name of a male character is put down instead of the name of the female character, and the sentence still has all the female pronouns. "Bob went to the store, then she went to the movies." It makes you wonder if they reread the book at all after finishing--the eye sometimes skims over typos, but c'mon, you ought to be able to keep your own characters straight.
