I find the main thing preventing me from building a viable quad copter is the ability to control 4 rotors at once. My keyboard can only handle 3 controls being pressed at once. So I can't run each rotor individually, which is what you need, in order to run the front two for forward lift, the back two for rear lift or the left or right sides for left / right turning.
You could use sawblades for basic power since they require no inputs to run, then use other controls for fine adjustment.