I noticed that my delegated calendars in my work Google Calendar account were not showing up in my iPhone’s and iPad’s calendar app. These calendars are shared calendars that I use for team meetings and so on. I keep them separate from my main calendar. I battled to find a solution until I found this solution in the Apple Support Forum:
Was experiencing the same problem. Was using Exchange calendars with delegates. I just updated my iPad and just received iPhone 4s. Delegate calendars do show on iPad but not on iPhone 4s. Exact same calendar account settings on both. Thought it must be some glitch in iOS5.0 for iPhone.
Decided to change iPhone back to GoogleSync for delegates. Just had to go to https://www.google.com/calendar/iphoneselect and choose which calendars to sync. Disabled my original Exchange account on iPhone. All sorted now.
It works! Problem solved.