so consensus here seems to be in favor of: locking at most or all times, especially when leaving it unattended for a while with two dissenting approaches taken by tramp, whose dirty and unmarked bike does just fine as a theft deterrent and seaweb, but he doesn't even lock his house. i can actually relate to seaweb. i spent two summers out on this tiny island called 'block island' off the coast of rhode island. people left everything unlocked, people hitchhiked. you could trust everyone and anyone since people who lived on the island were there precisely because that is the way they preferred to live in the first place; not to mention, you couldn't get too far too quickly since you were on, after all, a very small island. you're in a good spot, seaweb. though i've spent most of my life in nyc and baltimore, i've tried best to maintain and even import that kind of mentality here.
tough - i haven't had too much stuff stolen from me over my lifetime, but of the 4-5 times it's happened the only thing i miss out of all of them was the bmx bike that i scrimped and saved to piece together, bit by bit, but was stolen in a flash, unlocked, in front of a strip mall. i was 12 at the time and even then, didn't like the hassle of clamping down a bike. it's supposed to be mobile, instantaneously mobile, just hop on and go, but that very beautiful benefit applies to anyone and not just the owner.
well i'm on the hunt for a good luck. if you have a lock that you swear by because it's amazing in some way, please post it here and tell us why you think so. light and compact, but still strong enough to hold up to be bolt cutters is what i'm looking for.