DJC0 I have an iMac, and Air and an iPhone. I have BusySync installed on the iMac and use MobileMe to keep all my iCal's in step. Hence i only need one BusySync license.
True, i needed MobileMe to do this (at ~$99/year), but there are a number of cheap or free ways to sync iCal calendars to give the same effect. The beauty of BusySync is that it syncs between **Google Calendar and iCal**, something that's much harder to do without grief.
And BusySync has done this seamlessly, for me at least. I'm very happy to have purchased it, and i highly recommend it.
(Version 2.1.9)