Fix for orphan user 'guest'?
The user "guest" is never assigned to a server login, even on a fresh install it is classified as a SQL user without a login. As you can only set the SID of a login (upon creation), and not a user I don't believe that this is possible; sp_change_users_login does not work precisely for the reason that the guest account should never be mapped to a server login. As a result, the user "guest" is always an orphaned user. Probably not the answer you wanted though :)