Valleywag have done an amazing job assembling the data of who uses what to stay in contact with whom. If that made no sense, go to the article and see who's winning the Facebook, Friendster, Myspace wars. Perhaps it's Orkut? This is definitely a great tool for choosing your social network platform (a choice that either means you have friends or you live in a social desert). I find it heartening to know that one social network system does not dominate the earth. In fact, anyone talking net domination is speaking to their own blog echo.
ps. Yes, there are more networks in the world than those mentioned in the article, but I think they were going for market domination, not a total breakdown.