This is silly. Social networking requires critical mass, else it's useless. Something like 2% - 5% of users pay for freemium services.

So imagine if you had only 2% of your friends on FourSquare, or Facebook, or Twitter. Much less valuable, no?

Also, These companies can make far more money via other business models.

Users > Revenues for some consumer startups. Grow now, monetize later.