Now that these things exist...
...my husband has an idea: a courier service based on quadcopters. Their route can exist about six feet above a bus route, he says. And they can do things like deliver coffee and donuts and kidneys and whatever else a person needs quickly. "How rad would it be to have dinner delivered right up to our window?" he asks.
I completely disagree. The idea of a swarm of these things cruising two or three stories above our heads, unmanned and carrying bags of donuts and/or kidneys is terrifying to me. This is how a bad sci-fi movie starts out. We use them for good. THEN THEY TURN ON US.