Odd that this interesting question has not drawn an answer. This is an important workplace function. Ours uses a Windows program that allows for delegating proxy accesss. I did find these:

OS X Lion Server Help: Manage shared calendars
TidBITS Networking:
MacMost Forum | How Do I Use iCal To Allow My Staff and I To Share Calendars but Not Have My Alarms Going Off On Their iMacs?
Sharing calendars with others through iCloud
Check out that last link from BusyCal. I use BC on my iMac and really like it, but I have never used it in a shared environment. BC syncs seamlessly with iCal and my iCloud calendar.

This might have potential too:
Apple iCloud: Share Public and Private Calendars

But maybe somebody can write from experience.