Netflix and Pandora are largely frictionless experiences. If I spend the money and time to get in a cab in NYC to go to a restaurant that sucks, I'm upset. That's the problem that Yelp is trying to solve. I can't quickly "change the channel" with Yelp, or any sort of ratings for that matter. It isn't a technical or algorithmic problem, it's a human one that doesn't scale well. Quantify != Qualify.