http://techcrunch.com/2010/02/24/yelp-class-action-lawsuit/ On the other hand, Yelp doesn't really do much for big business. From a logical standpoint, one could argue that Yelp has an impact on small businesses that they don't have on large businesses. As Yelp expands, that impact expands. They are, if nothing else, a factor for small business over large business. I agree with you as to the causality. I haven't read the study; I might now. That said, I used Yelp on my road trip to find places to eat and was handsomely rewarded (I used Hipmunk to find places to stay and was punished mercilessly). Never once did I say "I'm going to hit Applebee's because I know it'll be good." I do the same in my neighborhood, even knowing the "shakedown" they do. If nothing else, Yelp and its ilk have changed the way we interact with businesses... and I think we're just starting to see the tip of the iceberg on this.