I've got a Kryptonite New York lock and a 7' threaded cable that I run through both wheels and connect to the lock. The bike rack I use is in a pretty visible location near a door with a security camera that is continuously monitored, so I feel pretty safe. My two main commuting bikes are worth more than $2,000 so I feel that I need a good locking system. I never leave my bikes unattended overnight. I keep my lock and cable attached to the rack at night so I don't have to lug them back and forth, but I keep a small cable lock in my seat bag in case I have to make a quick stop while riding.