Russian social network Vkontakte has more than 100m registered users

"Vkontakte - the most visited resources of the Russian-speaking segment of the Internet ( TNS Gallup ).
The share of the site for more than half of Internet traffic CIS ( Liveinternet ).
The site recorded more than 100 million users.
More than 21.5 million users come to the site every day ( Liveinternet ).
More than 2.5 billion pages open daily ( Liveinternet ).
Approximately 65% of visitors live in Russia.
25% of visitors - from Moscow, 18% - from St. Petersburg ( Liveinternet ).
58% of visitors aged over 25 ( TNS Gallup )."

Source:  Vkontake, retrieved 9th February 2011, translated by Google Translate

Note - amusingly Google translates 'Vkontakte' as 'Facebook'.  I've corrected this.
Update - VK, the English language version claims that the site has 112m members