For all those times when you want to find out which Exchange calendars a particular user has access to, use this script:

(in this example, we pretend our user is called Fred Bloggs)

ForEach ($mbx in Get-Mailbox) {Get-MailboxFolderPermission ($mbx.Name+":\Calendar") | where-Object{$_.User -like "Fred Bloggs"} | Select @{Name="Calendar of";expression = {($mbx.name)}},User,AccessRights}