Otto, one thing I have noticed when using the plugin is that information such as the "First Name" and "Last Name" don't get added to a new user's profile when people register using the FB registration widget. Only the username, email and password. Are these fields something you have considered and not included on purpose?
If allowing the registration of contributers (as I am), your going to want to attribute an post using their real name.
Anyway, the plugin is great and some obvious hard work has gone into it. Shines out among the rest!
You can see how I'm using it here: http://alpha.godboost.com/blog/