Yelp has 17m reviews and 50m monthly visitors

"Today the company has surpassed 50 million monthly unique users (as reported by their internal Google Analytics), up from 46 million the month before. And they have a total of 17 million reviews for venues around the world. CEO Jeremy Stoppelman says that the service is seeing a faster rate of growth for both contributions (reviews) and users than it has historically— in Q1, users wrote 2 million reviews, while most quarters average 1 million. In other words, even if some of these other services are gaining traction, it isn’t hurting Yelp."

Source:  Techcrunch, 4th April 2011