When I think of motion controls the first examples that comes to mind are Minority Report and Iron Man. Both of these movies use holographic displays manipulated by hand movements. Hollywood is attempting to portray the future of computing with these interfaces. Are they correct?
Motion input allows direct manipulation of on screen elements. As opposed to the abstraction created with current technology; keyboards, mice, touchpads. Many people are working on motion control. Microsoft is treating motion as a first order input device with Windows 8. In 2006, Jeff Han, a research scientist at NYU, invented a "Minority Report Style Interface. And the Kinect has inspired many to explore new UI paradigms to handle motion interfaces.
However, there is one intrinsic issue with all of these methods. They require larger movements to utilize when compared to keyboards and mice. This will cause fatigue and reduce the amount of time possible to use a computer. If motion devices can provide enough benefit to overcome this issue then they will take over. Otherwise we will be using keyboards and mice until the end of time.