Kufu - 1:44 am on Nov 21, 2010 (gmt 0)
If you, for some reason, doubt these numbers, you can test out the insane number of pageviews that Facebook has. Just set up a CPM ad campaign and watch the pageviews come in. It is somewhat scary.
This test won't give you any idea about the actual percentage of pageviews that Facebook has, but it will make the statistic a lot less unbelievable.