That sucks. My cousin has had 3 bikes ripped off in the past few years, but I wouldn't say he's vigilant about locking them up.
I just got a hybrid Trek 7300 with no suspension. It?s a $500 bike (I paid $240, depreciation is so wonderful), pretty nice, but I hope that it won't be too much of a target compared to a ?real? mountain bike. I?ve already started upgrading parts however (got aluminum handlebars and STX-RC ?rapidfire? shifters, now the front derailleur has got to go), and it would suck if it got stripped. An ?experienced? person carrying a chain tool and an allen wrench could make very quick work of it.