Sorry, Yahoo. Facebook is now the second most-popular website

In February 2004, Mark Zuckerberg launched Facbook as a small social network open to only a few universities. In January 2010, Facebook has attracted 133 million unique viewers in the US alone, according to online analytics firm Compete. That's enough to push it above Yahoo and into second place.

Facebook's sudden rise to become the second most popular website in the US really started last year. The social network almost doubled its number of American users from just under 70 million at the beginning of 2009. Yahoo, on the other hand, has slipped from its perch above 140 million viewers last summer and slid to 132 million in January.

This is the biggest change in the top standings since Google stole the gold in February 2008.

"Is Facebook’s next conquest the Google traffic throne?" asks Compete in its announcement. "While eyeballs are newsworthy, the real story is engagement, especially in the ongoing battle for those coveted big brand dollars. On this front, Facebook is second to none."

Compete also tracks "monthly attention" – basically how much of a person's online time is spent on a particular website. Last year, Facebook not only led the pack – with users spending more than a tenth of their Web hours on that one social network – but Yahoo and Google also lost momentum. They each took up about 4 percent of a user's time online in January, according to Compete.

Worldwide, Facebook-nation is more populous than the UK, Japan, France, and Germany combined. Among its 400 million members, half log in every day.

Overtaking Google in the users race will not be easy for Zuckerberg and Co. Google constantly rolls out new features – including its recent Facebook rival. (Of course Buzz, Google's social network, has had a very rough launch – including news today of a class-action lawsuit.) Plus, Google's core business, online search, has gained market share almost every month.

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