I wrote this little script using CDO against Outlook 2003. It will scan a named Exchange Server through every mailbox and every folder in every mailbox, looking for the Enterprise Vault flag 'Do Not Archive'.
Someone people use the Outlook Add-in and 'inadvertently' set the flag - so running this script will show which folders out there have this flag set.
Unfortunately, because it uses CDO you do get the annoying 'address book' pop-up issue that is a security measure on Microsoft's part.
I will work on a better version that doesn't use CDO :)