Kim Severson wrote a peice about trading fruit among neighbors. Along one of my running routes, someone has a pear tree. Last year, they put a basket with pears in it out on their fence telling people to take one. I did and it was delicious, free, and very locally grown.
On the other hand, I know someone who has a pear tree in their fenced-in back yard and had some person jump the fence and pick all the fruit off their tree.
Sharing is nice; stealing not so much.