Who is responsible for cleaning up leaves that fall from neighbor's trees?

This responsibility has long-standing tradition - the person that own's the property is responsible for cleaning up the leaves that fall on the property. While it makes sense that the person that has the tree should bear the responsibility of cleaning up the leaves that fall, society has taken the position that they do not want stranger's on their property and therefore do the job themselves.  I do not recommend under any circumstances that you sue the neighbor.  however, if you have a good relationship with them, you may ask if they mind picking up the leaves.  however, you get the benefit of having a tree block out sunlight/damage to your lawn.  Remember that you have to live next to this neighbor, so starting a battle will not be a good move.