I just launched my site, and when you use the Login with Facebook, it creates the connection and takes you to the register/login page, but that's as far as it goes. In some cases. It worked in Chrome on the Mac, but not in Firefox.
In Chrome, I registered and it created my account, but it doesn't actually log me in. It posts to Facebook that I registered at the site as well.
In Firefox and Safari, when I get to the login/reg page, I fill out the info, but it just refreshes the page and doesn't create an account at all.
techgrab.ca if you want to test it out.
System Info
JFBC 4.1.1
PHP Built On Linux DOMAIN 2.6.18-028stab095.1 #1 SMP Mon Oct 24 20:15:15 MSD 2011 x86_64
Database Version 5.1.56
Database Collation utf8_general_ci
PHP Version 5.2.17
Web Server Apache/2.2.21 (Unix) mod_ssl/2.2.21 OpenSSL/0.9.8e-fips-rhel5 DAV/2 mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/5.0.2.2635
WebServer to PHP Interface cgi-fcgi
Joomla! Version Joomla! 1.7.4 Stable [ Ember ] 24-Jan-2012 14:00 GMT
Joomla! Platform Version Joomla Platform 11.2.0 Stable+Modified [ Omar ] 27-Jul-2011 00:00 GMT
User Agent Mozilla/5.0 (Macintosh; Intel Mac OS X 10_6_8) AppleWebKit/535.7 (KHTML, like Gecko) Chrome/16.0.912.75 Safari/535.7