Sadly, it doesn't go so far as allowing you to disable it entirely, to prevent it being sold on. Should your iPhone be stolen, you can then send a message to its screen, or lock or wipe the handset and prevent anyone from getting hold of your sensitive data. So long as you have push email enabled on a MobileMe address, this service pings the handset, retrieving its location from the internal GPS chip and plotting it on a Google Map.
Apple's Find My iPhone service has long been a feature of MobileMe.
