(Weight of lock needed to keep bike safe)= 1/(weight of bike)
That is: the lighter your bike is, the heavier the lock you need to carry in order to keep it from being stolen. The implication is that once you get a carbon-nanotube bike, you'll need to carry a tank around to lock it up in.
With that being said, I compensated for the theft of the Cannondale Road Warrior I bought a month ago by buying a Felt Z8 and a chain lock that weights easily twice as much as the bike.
It looks like this:
Except that its red and (sadly) deficient in argyle. I was thinking of "camoflauging" it by giving it a really bad spray paint job and tossing it in the mud... but its a really nice looking bike.