[sly010]

Snatching would probably not be an issue. (Delivery guy would also give the "cargo" to anyone who claims he ordered it). They also don't have to throw it though the window. You know to the second when the drone arrives and it can just hover until you open the window and take it. And it's your window, not someone elses. After 2 minutes, your lunch goes back and you got a bad point on your profile. You would need to order to the right window and stuff, but you can build a window map of the city with drones. I think the hard part is regulation and licensing the airspace, not the technology.

[TeMPOraL]

I think flying within centimeter distance of a building could present some additional technical and safety challenge (wind, avoiding people getting their fingers sawed off by rotor blades), but the legal hurdles will the biggest problem, I think.

There is little safe space to fly over in cities - you can't just start flying over roads and pavements, because if any malfunction happens, you'll be dropping a 10kg high-velocity brick at people and cars. You'll need at least specialized insurance for that, and I'm not sure if anyone gives this kind of thing.