Users Creating Multiple Accounts Using Ultimate Facebook Connect

I’m concerned if there are any scenarios in which a user would create multiple accounts.

I am planning on forcing users to register with Facebook and allowing single click registration where the “Login with Facebook” button will work as a single-click register button for new users. If a user were to change there Facebook email, the next time they login to my site would that create a new account?

I think most issues would be solved by not allowing manual registration but are there other scenarios anyone can think of?