Out of interest, how effective is the Oz system? Anyone know?

I've never bothered with it, or the NZ system, but I had a friend who made the mistake of registering with the NZ version of the system while in Japan. All it got her was a lot of mail from the tax department and a single phone call (to the wrong number - they called her parents in NZ) four days later to check if she was ok after the Tohoku earthquake.