Sorry for the delay in responding to this. I just looked at your site, and I'm not sure where you placed the tag. It also looks like you're not using the standard JomSocial template. Can you try/test the following things, which should help narrow down where the issue lies:
* Around the {JFBCLogin} tag, add some extra text, like TEST{JFBCLogin}TEST. If properly stripped, you should see just TESTTEST. That will ensure that you are adding the tag in the proper file, but mean that something else is causing issues.
* If that doesn't display TESTTEST, check to see if there are any other JomSocial themes installed on your site and determine which one you are using. Then, ensure you are adding the tag to the proper themes' frontpage.guests.php file.
Finally, the FB / Twitter tab module in the right column at the bottom is re-including the Facebook Javascript library. I don't think that's the cause of the missing button, but it could be causing other conflicts. Can you disable, or replace that with the JFBCFan module (for Facebook feed at least) while you're testing. Once you get things going, you can try to re-enable the original again, but it's best to eliminate that as a possible point of conflicts.
Thanks,
Alex