The utilities are practically identical gui wise, and the following method of setting permissions works with both Exfolders and PFDAVdmin so this covers Exchange 2003 / 2007 / 2010.
Give a user permission to access all calendars. In this example Reception need to be able to edit all calendars.
Giving User1 access to User2’s calendar.
As you can see, Exfolders/PFDAVadmin are perfect for quickly modifying calendar permissions.