How much do reviews (good and bad) affect your choice of reading? If you see a bad review of a book you wanted to read, do you still read it? If you see a good review of a book you're sure you won't like, do you change your mind and give the book a try?
In general I'd say that reviews have some affect on my choice of reading, but not terribly much because what you like and what you don't like is really a matter of taste. A reviewer could say absolutely wonderful things about a book, but I might not enjoy reading it. Similarly, I might love a book that a reviewer thought was horrible.
If I see a negative review of a book I want to read, I'll probably still read the book anyway (unless the review is written by someone whose taste I trust implicitly). If I see a really positive review written of a book I'm not sure about by someone I trust, I'm more likely to pick it up. In a way, letting reviews affect your choice of reading is like getting recommendations from people you know. You are going to check out the books recommended to you by a friend who has similar tastes, where you just might smile and nod at the recommendations of someone else.