Two. I have a heavy U lock for any time the bike is going to be out of sight. I have a heavy cable combination lock for any time I am dashing in and out and probably have the bike in sight the whole time.

I use both locks if I have to leave the bike for a long time. Both locks may not stop a determined thief... but most likely they will look elsewhere.

I also ride a bike that looks like it has seen better days... that alone probably helps. Back for a year in my college days I rode a rusty stepthru frame bike with rusty fenders and a bent up basket on the handle bars... parked it on campus just about anywhere, with no lock. No one ever touched it. Sold it at the end of that year for a 6 pack. Internally the bearings and moving parts were in great shape, externally, it looked like it was all rusted together.

I don't leave my sleek shiny red bike anywhere. It attracts attention.

Where are you? There are no sign posts or parking meters to use? Then petition the businesses you patronize for a bike rack. Tell them that customers who arrive by bike spend more than people who arrive by car.

FBinNY is right: you only have to lock your bike better than the next guy. If you are in a low crime area, a cheesy little ski cable might suffice.

Zero. Crime is pretty low around here. I just throw down the kickstand, drop the bike by the door and it's still there when I come out.

Either a cable lock or a chain lock, depending on what bike I'm riding and where I plan on locking it. For 90% of my riding, a cable lock is sufficient to ward off the kind of crimes of opportunity my parked bike might encounter. If it's an especially sketchy neighborhood or I'm on my nicer bike, I'll use the chain.