Any idea how the lock was defeated? Was it left behind or taken with the bike?
When I do have to lock up my bike, I use the Sheldon Brown method (
http://www.sheldonbrown.com/lock-strategy.html), modified with the cable lock being run through the seat rails as well as the front wheel and frame (I have a quick release seatpost, which he doesn't recommend). I almost always remember to take all my accessories with me when I lock up.
Bikes aren't very popular here, so usually when I lock up my bike it's the only one in the area. That may actually be a bad thing, since there's no "easy target" bikes for the potential thief to take instead of my bike. On the other hand, the low popularity of bikes in the area may also mean there aren't a whole lot of people wandering around town looking for bikes to steal.
One day I had to lock my bike up outside and forgot to take my 3 Planet Bike Superflash taillights and Topeak Road Morph G pump off of my bike. That's alot of $ in accessories just sitting out in the open, locked to a handicapped parking sign in a park for about 8 hours. When I came back I was very happy to see everything was still there. On the other hand a friend of mine left his bike outside the parking lot access door to the apartment building he was living in when he went in to get something real quick, and when he came back a few minutes later his Cat Eye LED headlight had been stolen.