How much theft can one person do?
http://www.nytimes.com/2008/08/22/world ... anted=1&hp
There is a lock used in europe that seems interesting.
There is talk of a weakness in the lock keying design though.
http://austinbikeblog.org/2008/08/06/re ... heel-lock/
http://www.bike-eu.com/products/2911/ax ... -lock.html

There are some good locks out there and hardened alloy chains that are light for their strength and essentially cut proof in larger sizes.
GPS is now much cheaper and included on some new bikes.