I've been into the hobby (building, flying and racing multicopters) for about 10 months now-- I personally think it was a combination of factors with the bigges

I've been into the hobby (building, flying and racing multicopters) for about 10 months now-- I personally think it was a combination of factors with the biggest one being the advent of the tiny / cheap gyro and accel sensors mostly used in smartphones. The catalyzing event for the hobbyist side of things was the release of the Nintendo Wii-- since the wiimote controllers were a readily available and relatively cheap source of these components the hobbyist "scene" really converged around an open source project to hack together active flight controllers from wii controllers and arduino boards. These flight controllers are what allows multicopters to hover so effortlessly-- the computer does all the hard work of balancing motor speeds on the millisecond timescale. (If you could go back and give one of these boards to the guys at NASA in the 60's they would have called it cheating.) Obviously I've painted that with a very broad brush and people with different opinions will show up to tell me about how I'm wrong and a noob-- but this is how I see the history in a nutshell. Traditional model RC electric airplane components were also getting better and cheaper in conjunction with the birth of $20 flight computers. Faster and more efficient motors running on smaller better speed controllers, all powered by lithium polymer batteries that not only have great energy density and discharge capability but have become almost a commodity product thanks to modern consumer electronics.