Martin,
I get the example of zip code and city, though in this case I think the second user is the problem and you can't rely on another responsible user to be already editing every time this user tries to edit just a zip code. ;-) I've posted a few points in response in my other reply to Pertti.
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1
