In case you can't make out the fine print, the overall penetration rate of social networks in Latin America is a whopping 87.2%. This is for ages 15 and up, at home and at work, not including mobile access and Internet cafes.
I would argue, that based in high mobile phone usage in these countries, the percentage of social network users would be even higher.
Oh, and the most common social networks in Latin America? MySpace, Facebook, Hi5, Orkut and Sonico, according to comScore.