Is there a reason the user would need more than one account?
Some users may not remember that they have an account, and wants to connect with their Facebook account to leave a comment for example.
Also it will be faster for users to click on the button "Login with Facebook", instead of remembering the password for old account.
I think the use and connection to a geeklog site will change with version 1.8.0. With OAuth, you're putting up something more natural in the act of connection because a significant portion of users have a twitter or facebook.
I'm available to customise your themes or plugins for your Geeklog CMS