I'm really not that worried at school about my bike getting stolen. My current lock is better than most at school, and a lot of kids have better mountain bikes than me. When I get a evolution mini, I'll have the best lock at school.
One of my friends who rides BMX has this great bike with a $60 V link chain and a expensive crank. He locks it with a dollar store combo lock that I could break by standing on.
So I'm not that worried. My city is small.