We agree, the system plugin should have been called out more. Again, it was a late addition to 3.0.2, but it's been tested enough over the last month. It will be on the JFBC Overview page in the next release, and we just added it to the configuration guide that it should be enabled in the "Enable Plugins" section.
As for your current issues, in IE8 or IE7, I'm not seeing the Javascript errors you mention. As for this being a beta release, it's definitely not. 3.0.2 has been out for over a month now, had 2 RC releases ahead of time, and 2 very minor bug-fix releases after it went to 3.0.0 release. The Javascript error you mention above is actually referencing Facebook's javascript library (all.js), which Facebook is at liberty to change whenever they want. It's possible (and has happened many times in the past) that they pushed an update to their library that caused a conflict. Since we don't see it now, they also may have fixed it quickly. When they do push a conflict in their Javascript, we work very fast to fix it, which was part of the purpose of the 3.0.2 release, which was released within 12 hours of a Facebook API platform update which caused issues for JFBConnect users.
Again, we can't see that error in IE7 or IE8 and don't see any errors in Chrome either. Didn't test other browsers, but let us know if you're still having issues. We tested the login button to the point of allowing your application. We didn't not login, as we don't like creating users on everyone's site unless they want further debugging help.
Keep us posted on your status!