Maybe I am missing something, but... Take a group called "foo" with an SMTP address of foo@org.com. I need the group mail enabled to assign Public Folder permissions, so the group gets the email address foo@org.com. Initially the group is set to deliver to all members, but the group admin wants to change it to deliver to the group mailbox. In the background, the script would need to create a new user called fooMBX (can't create a user called foo because of naming conflicts), mail enable it, take away the foo@org.com SMTP address from the actual group, asign foo@org.com to the user account, assign permissions to the mailbox for the group (can't wait for E2k7 for Power Shell!!!), etc. This doesn't even take into account the Display Name for the GAL... I need the group in the GAL for permissions on Public Folders, but I also need the mailbox in the GAL for the users to send mail to it. Having a different name in the GAL for the mailbox would only serve to confuse and frustrate our users.
The only other option that I see is a mail enabled Public Folder, but I would hate to waste the time developing this when they are just going to go away in the future.
I guess I could also create the fooMBX account, NOT give it the foo@org.com address and only the foombx@org.com address, set the altRecipient LDAP attribute on the foo group (I see this is an available LDAP attribute for a mail enabled group) to forward to the fooMBX account. However, exposing this as an option to the group admins would be less than ideal (I just imagine one of them flipping it from forwarding to delivering just to see what it does). We could only expose this to our help desk, but that would be a business process change. I know we are probably not the typical organization, but this is why I like the idea that mailbox != user account.