BuddyPress.org

Manoj Kumar used to have a plugin to do this via CSV, but I’m not sure it works with BP 1.1+.

Check out these plugins:

http://manojkumar.org/user-import-for-buddypress/

http://manojkumar.org/bulk-import-members-users-plugin-for-buddypress-site/

You could probably hack it to work for BP 1.1 if it doesn’t work.

The only other way to mass populate your BP community would be to do it via mySQL or PHPMyAdmin.