I'm on Facebook, I would say I write a comment on average one a week (I infrequently login), I don't really see what it does beyond acting as a glorified address book. I think it's good for keeping in touch with people, but I pretty much hate the constant emails inviting me to goto events in the UK. It's also a good way to share photos but again I'm not sure about the privacy settings and who can see them, I don't understand it all really nor do I want to invest time in understanding it.

Some people clearly don't care, some of my brothers friends have some pretty risque pictures on there.