Facebook has knocked out Yahoo from its second spot on the ‘most popular sites’ list on the Web. Passing Yahoo with 133 million unique visitors in January, Facebook is now the second most popular Web site in the United States, according to new research.

A report from Web analytics Compete stated that Yahoo lost the No. 1 spot to Google just about a year ago in February 2008, and now sits in third place after Facebook took its spot.

Competes’ Aaron Preblud writes, “It's been two full years since we've seen a shakeup at the top. In February, 2008, Google overtook Yahoo as number one, and never looked back”.

However, Facebook rules the Web if we talk about the amount of time people actually spend online. “11.6% of all time spent online was spent on Facebook, compared to 4.25% for Yahoo and 4.1% for Google”, Prebluda added.

Does that mean that Facebook is now going to eye the first spot, rivaling Google? Prebluda thinks it is unlikely, though anything might turn the tables. He speculates that Google's recently announced Buzz feature could eventually affect Facebook's ability to "keep up” its current pace.