Meanwhile, it's adding about 250,000 new users every day. It currently has about 50 million active users, up from 12 million in December. Over half of its active members return to the site daily and some 59 percent of its users are outside the U.S.

A key driver of Facebook's user growth is its decision to open up its platform to third-party developers in May, which has allowed it to offer its users over 7,000 applications currently.

However, Google last week made a power move that could significantly neutralize the attractiveness of Facebook's applications. Google launched its OpenSocial program, whose set of common APIs (application programming interfaces) will let developers create an application once and have it run in multiple social networks, including, eventually, MySpace.

While it's generally acknowledged that the deep information Facebook has on its users can be a gold mine for its advertising efforts, social-networking sites also make marketers uneasy.

For example, the content on social networks is largely unregulated and created by millions of people, a situation that can lead to ads appearing alongside vulgar or objectionable material.

Social-networking sites have also gotten a bad rap for what some in law enforcement consider lax controls that lead to sexual predators stalking and victimizing minors.