social is a feature, not a destination
right now social networks are *sites* and/or web apps. you want to build a social network, you need to sign up to a site or install an app. of course, the social network is contained *in* the site/app. if you want to move your network - ha!
in the future, social networks will not be part of apps or sites, but part of the net itself. just like email is not an app or site anymore. email 'follows' you around. it's part of the net itself, not an application on the net.
and social networks will be part of the net, too. no one site or app will own the data. just like no one site or app owns your email (ok, gmail and outlook are kinda creepy...)
i'm look for the day when social is a feature, not a destination