To find all users in AD that have forwarding turned and enabled for their account and mailbox create a new saved query in AD Users and Computers and use the following LDAP query.
(&(mailNickname=*)(altRecipient=*))
This is very useful obviously if there a many accounts and you need to find all users that have had forwarding turned on for their account. The alternative to this is to select the properties of each user account one at a time and look at the delivery options configuration.
