Rated 5 out of 5 stars

@Bade, to get your TBird cal entries up to Google Calendar: In Thunderbird, right-click over the calendar you want to sync to Google. Select 'export calendar' and save the calendar somewhere memorable. In Google Calendar: Calendar Settings -> Calendar -> "Import Calendar". Select the file you just saved from Thunderbird. Boom. Done. Then set up a new Calendar in Thunderbird with the Google Provider extension and sync it with your Google Calendar. At this point, you'll have two identical calendars (hopefully) and the non-Google-synced one can go. Simple and very handy.

Excellent plugin. Simple to use. No problems here! Running Tbird 3.1.2 with Lightning 1.02b on Ubuntu Lucid.

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