This is a very interesting slideshow, well worth the 4 min it takes to read. I think it gives great insight into where Facebook, Blogging, etc. comes in. In short, people follow Maslow's Hierarchy of Needs in their usage of the internet. They want to feel secure, they want to be able to accomplish their task, then they move into higher needs like the need to be social (enter facebook blogging, chatting, etc).
Anyway, it gives a good perspective on where these technologies fit in.