The social network has added 50 million users in a little over three months according to CEO Mark Zuckerberg, and 100 million users this year, making it one of the fastest growing social networks on the Web.

The site says that about half of Facebook's users -- 120 million -- log on every day, that two-thirds of them are out of college, and that the fastest growing age group for Facebook users is 35 and over.

"The 250 million of you on Facebook today are what gives Facebook life and makes the site meaningful to everyone using it, so we thank you," wrote Zuckerberg, who founded the social network five years ago while he was a student at Harvard.

Facebook must still contend with challenges, though. Twitter last month was doing twice as well at attracting unique visitors to its Web site, although Twitter still has less than 20 percent of Facebook's hits -- 23 million versus 122.6 million in June.

Facebook users are also still heavily concentrated in the U.S. and Europe, according to a heat map that Zuckerberg posted in his blog, although there's been growth in India, Asia, Australia and South America, especially recently.

Capturing foreign users can be tough, however, according to one Chinese entrepreneur, Calvin Pak, social networks and the Web are used differently by people in different cultures, and Facebook is attractive to Westerners.

Pak, who was born in Hong Kong and educated at U.C. Berkeley, returned to Beijing last year and started Facekoo, a Chinese language social network for Chinese youth.

Facebook claims that 70 percent of its users are outside the U.S. and that the site is available in 50 languages.

InformationWeek has published an in-depth report on the current state of IT salaries. Download the report here (registration required).