Do you lock your bike properly? Do you really, or do you just think you do? Hal Ruzal from Bicycle Habitat (he co-founded it in 1978!) took a walk around New York City with our friend Clarence at Streetfilms and graded various locked bikes, pointing out what was done correctly and what was wrong with each of them. If only more people listened to Hal, the number of stolen bikes would probably be much lower (though proper locking isn't the only thing needed to solve the problem -- we also need more enforcement by authorities and more quality bike racks everywhere).
And this one from 2009:
And for something truly old school (in Internet-time, anyway), check out this one from 2003: