Our air control system has enough trouble managing the (relatively few) big airplanes on defined routes. Ubiquitous copters on random paths will be a nightmare. As these things become common and hobbyists adapt their own, we have the potential for small misguided devices to bring down hot air balloons and landing aircraft.
Here's a quadcopter bike
What I find most interesting about these videos is what they DON'T show. The last couple of seconds of the Domino's video implies that you just reach out and grab your lunch from the midst if eight furiously-spinning razor-sharp propellers! Can you imagine how this might turn out?
There's another way to look at this too- If you want a free Octocopter, just order pizza and have it sent to the vacant house down the street. Then as it comes down to deliver the payload, sneak up on it from behind and throw a blanket over it.