Another question is would they be a threat to birds?
The technology side is cool, but I don't relish the thought of looking out the window and seeing the air packed with delivery drones going to and fro.
Really - unless you lived on 5th Avenue downstream from a local delivery drone center, I doubt you'd see many drones. I don't see how we would see a sparrow flying past as 'pretty' and a drone flying past as 'ugly'. I would be amused to watch them from a window, just like I get amusement from watching planes take off and land. I guess it depends on your perspective.
A system-wide software glitch could also cause quite a mess in a dense city.
I think this could be cool but I would prefer my packages to be delivered by the Planet Express ship.