I must have registered for facebook a year ago and left it at that. I'd not even uploaded my photo and was in danger of forgetting my login details.
This week a growing number of 'friend' requests shamed me into returning and I've been impressed. Facebook seems to have reached critical mass. Among university students certainly, but also among the usual avid social networkers and including some seasoned professionals too.
As a networking site, it has the immediacy of IM and Twitter; as a content site it's less valuable though most people have posted extensive photo albums. If the currency of MySpace is music; and of blogging is ideas; then facebook's speciality is photos.
Why is it more attractive to students than blogging? Facebook resembles a pyjama party (it may feel daring but it's really very safe). Blogging's more like a nudist beach. You (and your lumps) are exposed to the stares or indifference of strangers. Not for everyone.