Hey K, I'm writing this here as the incubator site gives me internal error when I try to post.
I'm reading about what Facebook offers with their API.
In addition to the Login plugin they have the Registration plugin. From Facebook's Developers Site: "The Registration Plugin offers two key features not available with the Login Button: support for users without Facebook accounts and the ability to request additional user information that Facebook may not have or make available."
This is huge. For the moment new subscribers to my site who use the Facebook Login button, when they are not yet members, are automatically given an account that misses many fields. Not only that, I'm using a plugin that allows members to select from different account types, so if you integrated Facebook Registration, they could both select the type of account and fill out many other fields so that they will not have the confusion later on that they can't use their account till it's complete (I use progress bar to do that).
What I would do is first compare the user's Facebook ID to see whether they already exist on the site, if they do, they get the Login button, if they don't they can get the Registration plugin kick in.
Thoughts?