| My understanding is that since the key interacts electronically with the ignition (there's a more complicated test than just whether the key is the right shape or not), the MINI in it's base configuration is a very hard car to steal. I didn't even bother getting the security system on mine. A club, wheel lock, or obvious security set-up may deter casual fools who don't know about MINIs; but other than that I'm a bit skeptical of the benefit.
I've only ever heard about one being stolen, and that gentleman admitted that the perps took the key from inside his house in order to steal his car. | 
