Looking to create a community similar to facebook for your site? Buddypress might be the answer you are looking for.
Buddypress is a free, opensource, social community that runs as a plugin on the largest blog software, wordpress. Buddypress thus far is in its early stages of development with version 1.2.2.1 just being released. However, buddypress can be used for schools, businesses, or any online community.
Here is an example site: http://njsurfingclub.com/users
Buddypress site: http://buddypress.org