This was covered in our morning news today as well.
The general consensus from this morning's discussion was that the reason the people who don't give property back is because of their so called "busy" selfish lifestyle. They think it might be a hassle to return it, therefore causing them inconvenience. Those who were honest were usually those with more time to consider the implications of how the owner might have felt. All this goes hand in hand with the society they live in. Smaller cities and towns had more of a sense of community, larger cities create anonymity, therfore making the finder feel less responsible for other people's property. Others thought that if they did the right thing, the Karma would come back to them, so even if they did give it back, it wasn't for anything more than selfish reasons.
Personally I'd try and find the owner, usually there's a home number, or an ICE (In Case of Emergency) number in the phone. Same with wallets, or anything else - Give it back, personally. Handing it to the police if you can't track the owner in a suitable time frame.
Mick
