Social net-WORK-ing

I'm now starting to understand that some people in the west are hiring other people to do their social networking for them. I'm currently registered on three sites: draugiem.lv, Facebook and LinkedIn, and i start to feel the pressure. When it's only the closest circle of friends you're linked to, you don't feel any pressure, but when it gets bigger and you're getting invited by people whom you don't know personally, it gets tougher since, what's the point of accepting their "friendship" if you afterwards don't socialize with them at least on "small chat" level? 

Now, should i accept the friendship of the guy who invited me today, or just pretend i'm dead?