Only Microsoft, with 869 million unique visitors, and Google, with 970 million, stand in Facebook's way at this point. Yahoo drops down to fourth, though that should really come as little surprise--Facebook has been chipping away at the search giant for some time now.
As of December 2009, Facebook's pageviews were already up to 193 billion versus Yahoo's 100 billion (and Microsoft's 109 billion, to note). As well, November metrics from comScore indicate that Facebook serves up more than twice as much display advertising as Yahoo—23 percent of all online ads within the U.S. compared to Yahoo's 11 percent.
Facebook leaped over Yahoo in a batch of September comScore metrics related to U.S. video properties. As of August 2010, Facebook delivered video to 58.5 million users versus Yahoo's 53.9, representing a total of 243 million viewing sessions to Yahoo's 229 million. The only metric where Yahoo actually beat Facebook out was on viewing time—Yahoo users viewed an average of 31.6 minutes of online video per person versus Facebook users' 20.5 minutes per person.
Yahoo nevertheless beats out Facebook when isolated to just U.S. visitors only. In this, the company is the top website on the Internet with 181 million unique monthly visitors. Facebook, at 152 million, sits in fourth place on this ranking.
Narrowing the category to search engines only, Yahoo still trails Google at a rate of 16 percent to 66.2 percent for U.S. search engine market share. Its second place ranking is a bit tentative as well, for November 2010 metrics from comScore show that Microsoft, at 11.8 percent, is slowly gaining ground based on October 2010 results.
"Our greatest competitor probably is Facebook, more so than Google," said Yahoo CEO Carol Bartz at a Bloomberg event earlier this month. "They're a hot site, but there's room for more than one of anything."