I place an incredible amount of stock in public opinion. If 8 out of 10 people love a movie, there's a good chance I'll love the movie as well. There are a considerable number of factors that can distort public opinion, such as the conditioning that might initially cause first time Neapolitan tasters to find it wet or burnt, but, in general, in most areas, I trust the public.
These restaurant rating sites, like Yelp or Urbanspoon, though, are enigmas. I really thought they'd be useful tools for finding the best restaurants, but, time after time, I've gotten burned with some of the most atrocious food ever. The top rated pizza in my area on Urbanspoon has the texture of a dog's toy. It's confounding. Maybe, like IMDB with obscure movies, the ballot boxes are getting stuffed, so perhaps, as more people use these sites, the reliability of the ratings will improve. Right now, though... forget about it.