Since Apple's iCal stores data natively in iCalendar format, I was just going to apply a folder action to whichever calendar the user wants published. The folder action would detect any iCal file updates and trigger the execution of the java program that would parse the ics file and then, using the Java Client Library, publish to Google Calendar.

I had not yet thought about a true synchronization algorithm. My plan was crude - to delete all the data in the target GCal and then copy in all the events from the local iCal file.

Your iSync approach is much more sophisticated than my approach. I'll probably wait to try yours.