Looks like it is still appealing to those who are in their 20's, just like MySpace is appealing to the teens. I can't even join a university network without having a current university email address. D'oh, I should have kept my alumni email account. I guess for 30+ oldies like me, a LinkedIn profile would be much more useful. Sorry, I don't have time socialising, but please help when I am looking for a new job :)
Developers for Facebook, however, looks quite interesting. It provides a RESTy API and HTML-like markup language to build applications inside the Facebook platform. There are various client libraries, and even a Python module. It is a bit too late for me looking into all the details, but from a list of functions provided, they provide a great basis to create some interesting mashup apps.