It’s actually fairly easy to make your newsletter signup form run through facebook. This snippet (basically lifted verbatim from fb docs) shows you how to solicit full name and email address. Facebook then checks to see if the user is logged in and if so automatically backfills in the data for the form. If the user isn’t logged in to facebook the default text inputs are shown.
On submit you can tell facebook where to send the resulting data. In this class we are pointing things at web-op.com/fblogin.php.
You can view it in action here