Facebook beat Yahoo in unique visitors in the U.S. for January, becoming the most visited web site next to Google.  As reported in Mashable, internet analytics firm Compete.com measured a little more than 133.6 million visitors to Facebook for the month, beating Yahoo by more than 1.6 million visits.  The firm’s measures for December 2009 had shown Yahoo still in second place behind Google, with Facebook a close third.  For last month, Compete.com tracked nearly a million and a half fewer visits to Yahoo.   Meanwhile it saw Facebook increase by nearly that same amount, nudging up by 1.49 million unique visitors.  Mashable says the milestone comes after Facebook announced its 400 millionth visitor earlier this month.  Read more at Mashable.