I've still not found a good solution for clearing my clogged gutters, and I think someone should invent a gutter-cleaning drone. To my knowledge no one yet has, though a company called Aerones has created massive 10-foot-wide multi-rotor drones to de-ice wind turbines (warning, turn your speakers down):
Because the thing is tethered with both electric and water, it has no limitation on flying time or liquid dispensing, and you can keep it running until the job is done.
Having solved the problem of both payload and power, the company has expanded into a more pedestrian task: Washing windows.
The next logical application might be firefighting, if they could manage the water pressure. If they can't, I'm hoping they make a lateral move into gutter cleaning.