There’s a screencast showing how it will work. And it does exactly what I need it do.
Edit Google Calenders in iCal
So now I can make a shared calender in Google Calender, subscribe to it in iCal, edit it in iCal, and sync the changes right back to Google. Wonderful!
My next question is obviously if several people can edit the same calenders? I would guess this is possible.
But does Spanning Sync keep track of things, so if I edit a calender in iCal, and then try to sync it back to Google Calender, Spanning Sync will warn me if the calender has been changed between this and the last sync.