Let's say they somehow manage to perfect street landing, so that drones won't come crashing down on people, parked cars, construction sites etc, independent of weather conditions (snow, ice) - what happens then? Does the drone wait until you go down and pick up your pizza? What would prevent people from stealing a (rather expensive, I imagine) landed drone?

Does it just drop the deliverable from a safe distance? So what about "oh hey, there's a hovering drone, let's go pick up some free pizza".