AFAIK no one seems to have repaired on it so I will take the risk of classifying it. There are several kinds of social networking out there:

– Open social Networking
– Closed social Networking
– Personal social Networking

Open social Networking is promoted by Facebook lately, you build a network of friends and people not related with your network can see who your friends are (or at least a sample of them). It is true that you can limit the level of exposure to the public, but by default (which is how almost everyone uses Facebook) you are mainly a public being. Facebook exposes data because they know the more open a network is the more traffic and new users you get, and that equals money. It is not very sensitive with the users, but most users don’t really understand the problems related with Open social networking until they suffer from it.

Closed social Networking is more like Tuenti, Tuenti doesn’t exposes so much by default as Facebook does, although it is yet a kind of social networking that exposes you to non-really-friends, as most of your friends will be nothing more that people you see from time to time.

Personal social Networking would be like Plugtodo.com, in this kind of sites the information you publish about your contacts is only accessible to yourself but allows you to privately build a social network in order to improve your contacts and the experiences you share with them.

As more critics arise around Open Social Networking it is possible that with time people will tend to retire their content from extremely public networks supporting closed and personal networks… but who knows what the future holds?.