I've added some stuff to this plugin for a project that needed some changes, including:
- Some misc things that looked wrong in 3.1 -- sorry have forgotten the details
- A configuration option to allow all new users to be added to a specified group
- A bugfix for a problem that prevented the plugin from working because it was running before the profile fields were actually saved. I've changed it the hook from bn_auto_group_join to bp_core_activated_user, which has sorted it out. Not sure if this was because of the WP version change or some other bug, but it was a little tricky to chase down!
Happy to send my current file or a patch, though I did also modify the indentation of the file without thinking about it, so a patch might be a bit difficult to apply against anything except the current released version.