For many years, Sync Services has provided the backbone for synchronization of other devices to Macs running OS X. A change that was part of OS X 10.7.4 has apparently stopped iCal from pushing changes to Sync Services, breaking some very popular synchronization applications -- BusySync and Spanning Sync.
The Spanning Sync official blog notes that:
Larry, Byron, and I don't want anyone paying for something that doesn't work, so we've decided to take the drastic step of temporarily suspending Spanning Sync sales.
Over at the BusySync Google Group, the team notes that "any changes made in iCal will not be synced to BusySync. However, changes made on Google or other computers on your LAN that you are syncing with, will be synced to iCal through BusySync. So, the communication is one way -- BusySync can push information to iCal, but iCal won't push anything back."
BusyMac, the folks who develop and market BusySync, have some solutions -- upgrading to BusyCal, their product that replaces iCal and BusySync; stop using BusySync and just have iCal sync directly to Google calendar (iCal > Preferences > Accounts); or go through a workaround described here that takes advantage of iCal syncing through iTunes.
Regardless of the reason behind the changes in 10.7.4, John Chaffee at BusyMac notes that "... Sync Services is deprecated in Mountain Lion, so this may just be a hint of things to come. Everything is moving to the cloud." In other words, don't expect the old way of syncing to work going into the future.
[Thanks to Danny Greer for the tip!]