For the first time, Facebook replaced Google as the most visited Web site in the U.S. for a full week.

Facebook was the most-visited Web site in the country for the week ending March 13, Hitwise said, an online traffic monitor, in a report today.

For the week that Facebook was number one, with 7.07% of all U.S. visits, Google was right behind the social networking site with 7.03%, Hitwise noted.

It shows content sharing has become a huge driving force online, said Matt Tatham, director of media relations at Hitwise.

People want information from friends they trust, versus the the anonymity of a search engine.

Rounding out the top five was Yahoo Mail with 3.80%, Yahoo's main site with 3.67% and YouTube with 2.14%.

Though the traffic levels were close, Facebook's year-over-year growth far outpaced Google's that week. The number of visitors to Facebook spiked 185% compared with the same period last year, while Google's traffic climbed just 9%.

It's definitely a big moment for Facebook, even though they beat by a small margin, Tatham said. We've seen it coming for quite a long time.

Hitwise reported Facebook outpaced Google this past Christmas Eve, Christmas Day and New Year's Day. However, this month was the first time that the popular social networking site took the top position for a full week.