source site - Google Calendar: How to Sync Any Desktop Calendar with Google Calendar

As of yesterday's announcement of CalDAV support in Google Calendar, you can now sync your Google Calendar with virtually any popular desktop calendar for free. Not only can you enjoy your favorite desktop calendar software and still get the benefit of the web interface, but you can also sync any desktop calendar with any other across platforms using GCal as a go-between. Let's take a comprehensive look at how to set up bidirectional syncing between Google Calendar and your favorite desktop calendar—from Outlook and iCal to Sunbird and Thunderbird—for free.

this is quite a cool tip on personal productivity.