Although the plumbing has been in place since the summer, it's always nice to have an official announcement, and now we do: Google has gone on the record with its support for CalDAV syncing from iCal to Google Calendar. You can now gracefully sync your editable Google calendars with your (Leopard-only) iCal, keeping a local copy of those events in the cloud.
Granted, both BusySync (which adds Bonjour-based iCal synchronization between Macs) and SpanningSync (which includes Address Book --> Google contact sync) have been handling this task with aplomb for some time, and they offer something Google hasn't -- a nice GUI for picking your sync options. That too has been addressed: Google Code is hosting the Calaboration sync setup tool, a basic checklist of calendars to add to your iCal setup.
If you are syncing your iCal and gCal data via Google's support for CalDAV, let us know how it's going.