I have a local Evolution calendar, as well as a Korganizer calendar on a different computer, synced with my Google calendar using the iCal link provided at the Google calendar site.
As near as I have been able to find out (maybe someone will come along and enlighten me if I'm wrong), Google's syncing is one way. My Google can update my local calendars, but they cannot update Google's calendar.
There is third-party software that promises to enable two-way syncing, but I've never tried it:
http://gcaldaemon.sourceforge.net/usage16.html