I always think it's funny when car owners act amazed when I tell them I lock my bike without fear on the street. These are the same people who park a $20,000 car on the street.
Knock on wood... I've never had a bike stolen. Some pain-in-the-ass petty theft, but nothing too bad. Right now we've got two locked outside on the sidewalk. I did have a Cannondale bike burglarized from my basement in Cambridge many years ago. But turned out to be not such a bad thing. I bought my current bianchi with the insurance money (amazingly, I *got* an insurance check for it) and I've never looked bike.
Most bikes get stolen because they're poorly locked. I try never to lock my bike to sign posts because of sights like this:
It's a picture I took last year, but the sign post just blew over from the wind. They're not to hard to bust if you try. Alas, the city is getting ridding of parking meters and nobody seems to notice or care that bikers are losing the ability to lock their bikes securely on the street.