Yelp does not have a powerful network effect like Facebook, its main distribution mechanism was SEO via Google search. Unlike Google+/Facebook, in this case Goo

Yelp does not have a powerful network effect like Facebook, its main distribution mechanism was SEO via Google search. Unlike Google+/Facebook, in this case Google is in an excellent position to compete, if they smartly integrate a mix of user-written and Zagat reviews into Android and iPhone maps (it will take a better product manager than Marissa Mayer though- so the outcome is highly internal politics dependent)