It is common knowledge that Facebook user number is thriving. The growth is exponential and Facebook features 430M unique visitors per month (oct. 09).
According to insidefacebook blog, France penetration rate is around 24%, that is 15M people have a Facebook account, around 40% of UK population is connected, and 8% of Germany population at this is just the beginning.
What raised my interest is the growth of mobile usage, the usage from mobile devices is stupendous too:
Twitter, the other prospering social network seems to have been designed to be used embedded within SMS. Each twitt is a 140 character message, just the right size to be within a 160 character SMS plus 10 characters for overhead.
Japanese biggest Social Network Mixi has now 16M page views per month, 75% of the views in Q3 09 were made from mobile devices.
I believe, one can expect, all Social Networks to become more and more mobile focused as mobile connections provide: ubiquity, real time, and in the near future location. The strength of this mobile wave is so strong, that Social Networks will redefine themselves as primarily mobile players.