I deleted and re-added my Google Calendar from iCal and selected the delegates. Nothing improved. I rebooted and still could not see the delegates. However, I went back to (menu) Calendar > Preferences > Accounts > My Google Account > Delegation and clicked on the delegates again. They reappeared.
I then went to my actual Google Calendar (in the browser, not iCal) and added a new Calendar. I switched back to iCal and added the new delegate. All delegates dissappeared, again!
It seems like when your applying changes to your delegates they break in iCal. However, once all changes are done with, everything works fine.
A few things to note:
It's not necessary to reboot in order to restore the working order of Google delegates in iCal. You must exit iCal and force terminate the CalendarAgent process in the system monitor. When you re-open iCal the delegates slowly reappear.
Under the View menu you can choose to see all delegates and calendars by clicking Show Calendar List. A left sidebar will appear with all calendars and delegates.
By default your calendar will syncronize every 15 minutes. This can be changed under menu Calendar > Preferences > Accounts > Your Google Account under the Account tab. Nonetheless, you can force syncronize with the Cmd+R keys or clicking Refresh Calendars under the View menu.
Calendars can be filtered under the Window menu. If your calendars aren't showing up, make sure that Calendar is ticked under the Window menu. You can also use the Cmd+0 keys.
