Like quanticle said, social networking. You can't say, "fuck this, I'll just integrate with myspace instead" without getting laughed out of the room. Like it or not, Facebook's the only game in town.
My problem is that is not a real thing which can be monopolized. I promise I'm not being (intentionally) obtuse here. I don't understand which piece of an online offering requires Facebook. Maybe an example would help me.