I, too, have this issue. I can't imagine that I pick up on every single error, as I have never been a fan of studying sentence structure, so when I notice something, it seems like it would be a pretty big thing. I like to think it is not the author's fault, but more a publishing error. I can usually forgive one mistake, but after that, I start ignoring the story and looking for more problems. The most error-filled book I have gotten through in recent months is Sing Them Home by Stephanie Kallos - and I happened to pick it up after reading something about one of the editors. Barf, barf, barf!