Another option, if you have V-brakes and will only be in the store a minute is to disconnect them. When you come out side you'll know who stole your bike because he will be laying next to it, moaning.

Most of the time I do lock my bike, but there was one instance where I didn't. It was ba beautiful day and I rode my road bike to school. A felt F90, not a uber great bike by any standard, but it meant allot to me and I couldn't replace it. Well, when I got to school and realized I had no lock ... I took the wheels off and carried the whole thing into class. I used the same tactic that I've always used for doing something I know I'm not supposed to in plain view: Just act like you are doing exactly what you are supposed to be doing. When questioned by a security gaurd about it I think I mumbled something about centrifigul force, rotational vs. linear speed and a physics project. He had no idea what I was talking about and let me go about my buisiness. The teacher gave me a puzzled look as I put the bike in the back of the class, but never said a thing.

As for people who don't properly lock their bikes, I see everyone. Its just how my brain works. You go to lock up and think "they're going to loose a wheel, them a tool bag, he's going to loose his whole bike, etc ..." It just makes me sick to get to the rack in the afternoon and some 20-something female med student is crying because all she can find is her front wheel and U-lock. I've started to believe that basic bicycle safety, maintenece, and repair should be taught in high school, but I doubt that would ever happen.

-Rob.