I remember reading a story a year or so ago about the police finally catching one of the prevailing Portland bike thief rings. It was a bunch of homeless druggies who would roam around stealing easy-to-get bikes, riding them to another part of the city and just locking them up on a bike rack for later storage/sale. After they were caught, they admitted they had done it to hundreds of bikes, sometimes not even remembering where they stored all of them. Every time I see a bike sitting for a long time in a strange location, I assume it is stolen and someone, somewhere, would love to have it back. I couldnt imagine taking it myself.

Unrelated story - when my brother was in college, his front wheel was stolen a couple of times. Turned out there was a gang of meth heads who would do the rounds through the college towns (Eugene, Corvallis) once or twice a month taking all the front wheels of bikes. They cut them up and sold them as scrap. They caught those guys, but there are so, so many more scumbags out there...