theres a software called Spanning sync its for MAc user who has Ical and use Google Calander.... its a nice program.
http://spanningsync.com/from the webite...
Between multiple Macs. Share calendars with your coworkers, family, and friends. And while you're at it, connect Google Calendar to your iPhone, iPod, and other devices.
What if you could combine Google Calendar's powerful sharing features, Gmail integration, and notifications with iCal's beautiful interface and offline operation? Now you can.
With Spanning Sync, your iCal calendars are kept in sync with Google Calendar, which means you can use the best features of both to manage your schedule.
Supports Google Apps for Your DomainSpanning Sync offers full support for Google Apps for Your Domain. So whether your organization is a one-person company or a 40,000-person university, your enterprise calendars are seamlessly connected to your Macs.
for me the Google Cal is kind arkward for me to use but i rather to use ical. with Spanning sync. any change i make in Ical are uploaded to a Calender in GoogleCal. and other people who has access to my GoogleCal Sharing, will see the change i made and if they make any changes to their Googlecal, i will see the change in my ical, thanks to Spanning Sync.