I’ve had a rather bumpy relationship with SpanningSync, and as a result several friends have recommended I try BusySync 2.0 beta. I’m very glad they did.

BusySync works differently than SpanningSync. Instead of a service, it works directly with Google Calendar with no intermediary service. It does not suffer from any of the issues I had with SpanningSync (forgetting to sync, forgetting which calendars to sync after an upgrade, stopping working when an upgrade was required – BusySync has Sparkle built-in, and alarms sync).

I’ve had two issues with BusySync so far:

1. A “BusySync Conflicts” calendar has been created a few times on my Tiger desktop; this contains events that BusySync apparently isn’t sure what to do with. I haven’t seen this with either of my Leopard machines, so it may be a bug/issue with Tiger.
2. One of my Leopard machines stopped syncing for a time entirely. I tried the “Reset Sync History” options, tried unchecking and rechecking the calendars to sync. It stayed broken for about a week. Finally I deleted all of the calendars locally, reset everything, and re-added them from Google. Since then, smooth sailing.

If you need to sync iCal and Google Calendar, I recommend using BusySync based on my experience so far.