[mingdingo]

The monetization need not be direct (i.e. charging people to use the site). It could be better ad placement, a search engine that knows more about you than google does, monetary transactions (auctions, payments), as well as other stuff...

Like it or not, facebook has real utility (just like central park), and people are willing to pay for real utility in one way or another.

[gaius]

What I'm surprised they haven't done already is extend their event planning mechanism to partner with ticket agents, train companies/airlines, cinema chains, restaurant booking systems, pizza delivery, etc etc.