I've had bikes with hard bags that lock, and bikes with textile or leather bags that have no locks. Although I have sometimes worried about it, I have never had an actually theft from my bike. When I park my bike I do remove the Garmin GPS and the I-Pass and take them with me, but everything else remains on the bike (good quality rain suits, miscellaneous items like bungee cords, a flat tire kit, first aid kit, etc., all in leather non-locking saddle bags. I often see riders leave an unsecured helmet on their bike, and I'll admit that I have done the same occasionally, and have never lost a helmet or even heard of someone's helmet being stolen. Any one ever suffer an actual loss of things from your parked bike?