Ahh.. one final bit of information. We don't have, and don't plan to add, a captcha to the Facebook registration process. Since the user has already been validated by Facebook, there's not much of a reason for it. We've never heard of spammy accounts created through Facebook users, because they can be too easily traced back to Facebook (not a throw-away email account like most spammers).
Hope that helps explain.. if you really need captcha though, there are some plugins for Joomla which can be added to any form, including our registration form. We can help point some out if necessary.
Thanks,
Alex