Yelp is IPOing today at $15 a share, allowing it to raise $123 million on a valuation of $900 million — $400 million more than it was apparently offered by Google a couple of years ago.

We know from the S-1 that Yelp earned $58.4 million in net revenues in the first nine months of 2011, representing 80 percent growth over the first nine months of 2010. It also has 22 million reviews, and sees 61 million monthly users.

During the first nine months of 2011, the company claimed 19,000 paid accounts — up 75 percent from the same period in 2010, And 529,000 claimed pages — up 114 percent. Its ability to convert claimed pages into paid accounts is going to be where the action is.

It must also continue to penetrate deeper into restaurants, amid tough competition from Google/Zagat and others. At the same time, it must continue to expand beyond restaurants deeper into shopping and services.

Restaurants and dining now make up 23 percent. Other major segments include shopping (23 percent), home and local services (10 percent), beauty and fitness (9 percent), arts and entertainment (8 percent), health (5 percent), night life (4 percent), and travel and hotel (4 percent). It also has a broad demographic, with 42 percent between the ages of 18 and 34, and 33 percent between the ages of 35 and 49.