According to new Hitwise data, 7.07% of all internet visits go to Facebook. Google is the second largest at 7.03%. And Yahoo is a distant third at 3.67%. Equally impressive is how quickly Facebook has gained on Google - since January, they have jumped from ~6.5% to ~7.1%. Much of that acceleration happened in the last thirty days. Just a year ago, Facebook represented ~2.5% of visits.
This data comes a few weeks after Compete released their January report where Facebook surpassed Google in aggregate visits. Furthermore, if Facebook now represents greater internet share by visits, you would imagine that they are therefore significantly ahead by time on site. Google's in-and-out experience combined with Facebook's single-page structure likely result in Google winning the page-view war.