As someone who studied sociology, I like this NESTA interview of Richard Harper, Principal Researcher at Microsoft and a sociologist by training. He quotes the Canadian sociologist Erving Goffman who said that there are front stages and back stages even in the same room, so when Mark Zuckerberg says that Facebook is the front stage, or the main representation of the self to others, he is misrepresenting what Facebook is about as it is just one of many ways of representing yourself.
Interview with Richard Harper from NESTA UK on Vimeo.