Hi Otto (and anyone else!)
Great plugins, currently using FB & TW versions but I have hacked into the comment box to use it for a charity that want to have users share a message after they have donated, and post what is essentially a version of a comment after being authenticated by wither FB or TW.
The issue I have is the comment box is ever present, and allows users to post a comment without authentication.
If I make it that comments have to be registered, it seems the plugins, while they authenticate you, they don't completely register you in the WP system.
What I was looking for was a hook of some kind that was returned when the user is authenticated by either plugin that I could use to display the comment box, like...
if authenticated, show comment form, else hide.
Hope this makes sense?!