Actually the user-base and workings of Facebook has changed dramatically since they "opened up" their network. You no longer have to subscribe to a specific network as mentioned in the article. And you are not limited to only talking to people in a given network, you can reach out to anyone (although on Facebook the majority of people have their profiles set as private).
And it is now estimated that as many as 40-50% of the users of sites like Facebook and MySpace are over the age of 30.

