Short, worst-case answer: Google web calendars no longer syncing with Microsoft or Apple's local ones. There are finer points and some exceptions, but that's the basic bottom line.
It remains to be seen. Google has said that they will "whitelist" certain developers to continue using CalDAV which is what iCal uses to sync both the Mac & iPhone. One would hope/expect that Apple will be one of those developers.
No one from either company has commented or confirmed it either way. It's a major reason why people are so surprised and incredulous about Google moving away from the standard.
