If I was a developer of social networking software, I’d be a little nervous right now.
BuddyPress is essentially a set of WordPress MU-specific plugins that switch Wordpress MU (Multi-user) from a blogging platform to a social platform, with features like:

Extended Profiles
Personal Blog
Private Messaging
Friends
Groups
The Wire
Status Updates
Albums

It’s pre-Beta right now, but given how easy and powerful Wordpress [...]