Why doesn't collaborative filtering work for popular review sites? The Netflix recommender is pretty solid. Obviously you aren't likely to have reviewed 200 r

Why doesn't collaborative filtering work for popular review sites? The Netflix recommender is pretty solid. Obviously you aren't likely to have reviewed 200 restaurants in Yelp, but it still seems like it would be effective if you had 10-30. But if I could go to Yelp and have it recommend restaurants based on my past ratings (well I have none now), that would be nice. I'd even take it a step further. I want recommendations of actual dishes.