Clarence - 9:19 pm on Sep 14, 2012 (gmt 0)
Facebook been took over Google for Impressions. Just not all impression were tracked "Mobile App, API calls, etc". Facebook is the largest Traffic site in the world. 700 million real active user logged in almost all day, checking constantly.
People are constantly logged through mobile apps, desktop app, etc.
A ton of traffic, and all User Generated.