Rated 4 out of 5 stars

Works great with Google Calendar.
64-bit version for Linux worked with this link (running Thunderbird 3.1.7):
http://releases.mozilla.org/pub/mozilla.org/calendar/lightning/releases/1.0b2/contrib/linux-x86_64/lightning.xpi

This review is for a previous version of the add-on (1.0b2).