Rated 5 out of 5 stars

Signed up for an account just to review this. Really awesome add-on. Does exactly what it says.

As @SukiLou said, check out http://bfish.xaedalus.net/2007/04/stay-in-sync-with-gcal-and-thunderbird/ for details on syncing up with Google Calendar.

The main thing that didn't seem obvious to me is that you need to create a "new calendar" in Thunderbird, and that is where you put in the Google Calendar info.

This review is for a previous version of the add-on (0.7).