Icaughtu, an app for a jailbroken phone, takes a picture (without the person knowing it) when an attempt to turn the phone off or when an attempt to circumvent the PIN screen and emails it to you with GPS coordinates. So, the phone effectively can't be turned off unless the SIM is pulled out giving the user some time to track the phone down and a pic of the person that stole it.
The fact that Find My iPhone can be twarted with the off switch is some what indicative that Apple didn't design it for theft, but accidentally losing it in your car or inside your home.
I use iCaughtU as well. If you have a CDMA phone it's pretty perfect since there is no sim to remove.