I think a lot of people here tend to project their feelings about bikes onto others. For us, if a bike is stolen, it can be like losing a member of the family (well, at least like a gerbil or something). I think a lot of of the kind of people that buy a bike, lock it outside without ever riding it and let it rust into oblivion are the same kind of people who might notice their bike is missing, get angry for about four minutes, feel glad for two minutes that at least they won't have to walk it to the dumpster when they move out and then move on with their lives. Not saying it is absolutely right to steal abandoned bikes, but rather that a lot of people make it out to be a much more black and white issue than it is.

We could ponder hypothetical situations forever but in the end all you can do is ask yourself if you're going to feel like a ****head for taking the bike. If it's a $50 Wal-Mart special and you know it'll make some poor child sooooo happy on their birthday and you know the owner moved six years ago and you were the best man at his wedding, ****head factor is probably low. If you watch some guy ride to and from work on a bike every day and you decide to clip his crappy lock and sell the bike on eBay, hopefully the ****head factor is sky high. When it falls somewhere in between... only you can make the call.

(FWIW, trying to approach the problem from a legalistic standpoint is likely fraught with just as much trouble. Just trying to take into consideration the vast variation between municipalities and their property laws would make your head spin, and that's without even trying to decode when it is or isn't ok to take abandoned property.)