While I'm new to this bike thing, I've noticed some odd ways people lock their bike. As I was loading my panniers with groceries, a woman pulled up and locked her bike to the next rack over with a chain. After she walked away to enter the grocery store, the bike fell over, stretching the chain so it hung just a couple of inches over the ground. No U-lock.

I do see more people though U-locking the bike to rack/sturdy something, and using the chain to lock the wheel to the frame, or take the front wheel off and lock it and the other wheel to the frame with the chain/cable. I have yet to see anyone putting their U-lock around the chain.