Tim Bray is having iCal problems at the same time as I am. I'm not convinced they are the same problem, but perhaps have the same root cause – bad design.
Perhaps it is just that synchronisation is a hard problem. Who knows?
All I know is that one of the half-dozen Macs I use from time to time decided to nuke about three weeks of calendar data – and that, as they say, just isn't cricket.
So I have begun to migrate my primary calendar data into Google's calendar. As a bonus I can now allow my wife to edit the shared calendar. I will continue to use iCal to view my calendars, as well as print them out for the fortnightly (if I remember) hard copy posted on a cupboard door in the kitchen.
Will I continue to use iSync? Yes, but with a closer eye cast on what's happening – I don't want a rogue data deletion being propagated to all my other machines again.