Re: Extended Profiles on Sign up?
WordPress MU and Buddypress have separate profile/user management tables that aren’t synchronized and in some ways clash. End users will see different profile editing screens, in wp-admin and buddypress front-end, with different data that have nothing to do with eachother. Users are identified by full name, username, nickname, blogname or whatever depending on where in the system you are and how it’s configured. It’s a confusing mess and my pet peeve.
But I’m not even sure if that’s relevant to your problem, so I removed the rant.