In June 2011, Facebook received about 870 million unique visitors, which exceeds the number of its registered users by about 120 million. It is because many of the site’s pages appear in search results and usually are visible to non-users, if only partially, according to DoubleClick.
The data showed that Facebook got about 1,150 pageviews per visitor, which implies it’s an extremely sticky website.
YouTube was the second most-visited site, with 790 million unique visitors in June and 100 million pageviews.
The data does not include adult websites, ad networks and certain sites owned by Google.