I'd be lying if I said I'd never collected any "obtanium." However I'm very selective and restrictive. I'll grab a business card or a piece of silverware if there's hundreds of others just like it as a memento - that doesn't impact anyone elses' enjoyment of the space. In terms of larger items I've only taken very few things.

I grabbed a classic ceiling lamp from an abandonned apartment building. It'd been abandonned for several months and slated for demoltion. I visited the block pretty reguarly for a few months and noticed ever increasing signs of vandalism. Finally when lots of things were turning up smashed or missing I decided to take it.

Aside from that I leave things alone, even when I desperately want them. I have my eyes on some items in the basement of a building slated for demolition. I'm leaving them alone for the moment, but if the wreckers arrive and the stuff is still there I will save it, but not until the last possible moment.