yeah i've seen that video and it blows my mind. I don't know if I would necessarily confront a thief, but I would probably at least call the cops. Or maybe just yell something out like "HEY, YOURE STEALING THAT BIKE" that way everyone would turn and look and the guy would probably run away.

Unless he pulled out an M16, in which case everyone is ****ed

In Austin, it seems like most bike theft occurs at residences of some sort. I like to think that if someone was jacking a bike outside of like Whole Foods, that people would say something...but I donno...