Facebook's "rolling thunder revue" continues as the 600-million strong social network is fast becoming the globe's dominant social network as the graph below from ComScore demonstrates. Countries that have leaned towards other social networks such as Orkut, Hi-5, Bebo, RenRen, etc. have obviously fallen for Facebook's siren song as they have support for 70+ languages...including Pirate. Seriously.
There will always probably be some regional, cultural and geo-political reasons for multiple social networks to exist, but I'd be foolish to bet against the Facebook juggernaut losing any steam as the social software of choice for planet earth. Hey, they rolled over Friendster and MySpace in North America long before your grandmother started her profile. How can your great-aunt in Hungary resist?