I fly really BIG rc airplanes. I have a quarter scale J-3, a quarter scale PA-18, and a 1/5th scale DeHavilland Beaver. They range in weight from about 15 lbs for the J-3 up to 22.5 lbs for the Beaver. 110" wingspan on DHC-2, 106" span on the Cubs. They can fly further than you can see them, if you really wanted to do so. The same radios are used to fly a large segment of the multi-rotor fleet, too. These quadcopters can fly out of line of sight with some relatively inexpensive radio gear. Cameras, both still and video, can be fed in realtime back to the pilot so that you can operate them in a "First Person View" format. They make great camera platforms, which is in large part why they're so popular. They're also quite easy to fly compared to airplanes and traditional helicopters, which further adds to their numbers. Most are "charge and fly" types, even the very expensive versions. There's very little actual building with them. The multi-rotor kits are generally geared toward the hardcore hobbiest who will select a gyro board, motors, speed controllers, props, etc, to get the best flight times, speed (some people race them while wearing goggles with a live video cam feed) etc. The toy type quads are just toys. But they still do all the flying for the owner. Saying you're an rc pilot because you can fly a quadcopter is like calling yourself a computer programmer because you have a Facebook page. The insanely cheap cost of this technology is making it nearly ubiquitous, and the ability to get cool aerial footage of just about anywhere humans are able to go is too tempting to people who make bad choices. I've been flying rc since 1989, when I was in college, and I hate multi-rotors, quadcopters, whatever the name. I abhor the word "drone" used in conjunction with these things, though. I don't know if I want a registry for them or not. There's good and bad with that. Mostly bad. I recon there will be a lot of interesting events in the near future which will determine what happens with the FAA.
https://www.faa.gov/uas/ <-- Some good reading right there.
The people who are following the Model Aircraft Operations rules are *NOT* the same ones that are getting in the news with their quadcopters.