BuddyPress.org

@anointed, if you wanted to just make it so you’re grabbing the user list of a blog instead of the members list, that’s very possible to do. But you will still probably want your root blog to be the center of all members.

Like andrea_r said, I imagine that MU is in a feature freeze at the moment until 3.0. All the devs are going to have their hands full rearranging the code to make it fit into normal WordPress so it’s a smooth transition for everyone.