In recent days, I've received a swarm of Friendster requests from people in the Philippines, mostly young women. I rejected them all.
Usually, I tend to approve most anyone requesting a connection through the main social network services. I have few restrictions and use friend connections as a way to bookmark people -- in the social network services, I can keep track of there where- and what-abouts, and in a pinch, I can contact them through those channels.
In MySpace, I reject requests also -- unless they're really people I know or musicians I might find interesting. Accepting musician add requests is a way to support their music even if you haven't connected with them otherwise.
Does that approach make those visible friendships meaningless? I don't think so. But how do you use social network services? I think the choices we make are more nuanced than many people studying the social dynamics of the Web might realize.