At the recent F8 conference Facebook revealed that they now have 800 million active users. Europe, with Russia included, has a population of 727 million. We now have a social network that is so large that it could fill up a major world region with people and still have some to spare.
Another comparison is that Facebook now has as many users as the entire Internet did back in 2004, the year Facebook was founded. Here are some other size comparisons you can make.The Presurfer