My hot-tub-running neighbor took it upon himself to trim my tree this morning. It must have been hanging about a foot over the property line, about ten feet up. Sure, he's not interested in picking up the hundred or so bean pods that his tree dropped all over my yard - but we better make sure that no tree limb penetrates the invisible plane of the property line.

Oh, I've also seen him picking up bean pods from my tree that were in his yard and throw them into my yard.
I'll say this, though. He's not a jerk about trimming the tree. He's asked me about it, and I've told him it's cool. He just goes and does it, and he doesn't complain about it. I just find it a bit annoying that he doesn't seem to care that his tree makes a mess in my yard.