How can I diagnose or fix the CalendarAgent occupying a whole CPU on Mountain Lion?

I am still looking for a solid answer.

In the meantime, I have the following script running in AppleScript Editor. This script looks for the CalendarAgent every 15 seconds and kills the process.

This renders calendar syncing unusable, but at least I can use my Mac again. I will let this run until I find a permanent solution.

The script is:

repeat
  set app_name to "Finder"
  do shell script "killall -9 CalendarAgent"
  delay 15
end repeat

May have to kill and rebuild Calendar db:

1. Disable the Calendar service from your account in System Preferences → Internet Accounts

2. Remove the preferences/database files for Calendar:

   rm -r ~/Library/Calendars/ ~/Library/Preferences/com.apple.iCal.plist
   

3. Re-enable the service.

^{Source: http://robert.accettura.com/blog/2012/08/19/how-to-stop-calendaragent-from-eating-cpu/}

Using Google delegates definitely caused the high-CPU problem with me.

The simple solution is to:

1. Uncheck the delegation w/in Calendar's Account info window (as indicated by the UPDATE above)
2. Change your Google calendar sharing by selecting the desired calendar(s) within the Google Sync Settings page: https://www.google.com/calendar/syncselect

Making this change eliminated the high-CPU problem, without needing to resort to the kill-the-CalendarAgent approach.