I have played with it. An example of it is by the WordPress meetup guys who have made a forum over at wpaustralia.org it is all BuddyPress. It is kinda easy to get up and running out of the box on a WP site, just install the plugin and away you go.
Thanks Pete, looks a bit plain jane to me, i guess their motives are a bit different than most folk who use Buddypress, i'll have a look on google to see some more examples, surprised no-one here is using it