Charge corporate customers all you want but if I ever pay as a user, I'm out. Make current free features paid? I'm out.
Roll out new features and charge for them? That's fine.
M. Zuckerberg seems like a smart guy who is passionate about the product - product guys aren't usually asswipes. Really interested in seeing where this goes. Also, far as I know, there are no proven models for monitizing human interaction in real lide, let alone in the virtual world. Traditionally, we've focused on charging for experience, not interaction.