The Internet is very effective as a peer to peer network. Peers enter into a conversation with each other. That conversation is creating a world filled with new possibilities. Text-messaging, gaming, file sharing, blogging, most email, chat rooms and social networks are all part of the wide peer to peer activity on the Internet.
If you are recognised as a member of a social network, you may be chosen by your peers to join another group they are forming.
If you understand the Cluetrain Manifesto, you'll know that to be invited to the conversation other people are having is a recognition by them of your status as a member. Members show each other a certain respect. They care that they don't give others bad or unreliable information. To do so would harm the reputation for good sense, reliability and helpfullness that they are trying to build.
In a social network there are places like guestbooks, commendation systems, friends lists or other ways that people can leave a trace of their interaction with you online. Over time you can see the cream slowly rise to the top. Those who are recognised by many people usually deserve their status. Like attracts like. Read the guestbook comments and you'll get a good idea about the sort of person this is.