Another important step forward for all who are looking for alternatives to replace Outlook. With latest Thunderbird 2.0rc1 release it is now possible to add calendaring capability to Thunderbird (using the Lightning add-on) with Google calendar synchronization that works even with iCal invitations :-). Really nice.

The author's blog at http://bfish.xaedalus.net/?p=239 seems to be down, but cached version is available.

Credits and thanks to Joel for finding it.