I just upgraded to SP2 RU6 on Exchange 2010. According to this article I should have been able to set retention policies for Calendar and Task items, but I don't see the option in EMC, and I don't see a registry key forELCAssistantCalendarTaskRetentionEnabled.
Did I miss something? Should that key be added, as in this thread? This is a Windows Server 2008 R2 system.