I had 2 stolen from me during my lifetime, luckily neither were particularly valuable. Learned my lesson thoroughly though, so now at home I keep my bikes inside in my living room, at work I now park in my company's underground parking which has regular security guard patrols and live monitored security cameras with a U-lock and cable.
So far so good. At the very least if someone steals one of my bikes I at least have 4 others I can hop on. N+1 has it's uses right?