Synching Google Calendar with iCal and Thunderbird

Via the CalDAV protocol, Google now supports bi-directional(!) synchronization between Google Calendar and iCal or Thunderbird. Details [source: fscklog]:
This is great, previously one needed the purchaseware BusySync to do so (note though, that BusySync also allows you to sync iCals in a WLAN).

Related post: Cloud-sync your iOS calendars (bonus: PC/Mac)