BuddyPress is still a relatively new plugin suite. It currently offers webmasters the ability to run a highly functional social networking site. However, there are some features that are still missing, including privacy options (ideal for the Slayers, who don't want their Watchers spying on their every move), a photo-sharing feature, and closer integration with other social networking sites. The good news is that all of these features are currently being worked on and BuddyPress is advancing quite rapidly.
The best place to learn more about BuddyPress is on the BuddyPress.org web site. The community on there is very helpful and the documentation in the codex covers most common questions. You can also download the latest builds of BuddyPress from the trunk, although you should use those builds on a testing server only, and not in a production environment!