I think it's pretty obvious that Facebook has been, from the start, something very different. It is so ingrained in every little design decision and how they promote and talk about the service that it is a tool for managing your public persona. Not a simple communication tool, or replacement for email. Though they obviously offer that kind of functionality as well through Messages and Chat.
Facebook wants to enhance or maybe even change the way you interact socially. It's not a political agenda, but it is definitly a very conscious mission to change a large part of western culture.
There seems to be a lot of confusion about this. So let me state it again to make it clear:
FACEBOOK IS A TOOL FOR MANAGING YOUR PUBLIC PERSONA.
You are profoundly fooling yourself if you think that most Facebook users aren't using it as a way to CC a list of people some photos. I don't know anyone outside of the tech/blog scene who uses Facebook to manage a public persona. It's just a different way to communicate with people.
FACEBOOK IS A TOOL TO MAKE YOU (the user, their product) MORE MARKETABLE TO ADVERTISERS (the customers).
By knowing everything about you, they can get better rates from advertisers. Everything else, like photo sharing, and the ability to send messages to other people, or check into place, is designed to get more info about you, and to make sure you don't wander off Facebook to their competitors (if you didn't have picture sharing, you'd be using Picasa or Flicker more -- and that might threaten facebook).