Yaw, pitch, roll via 3 axis gyroscope.
X, Y, Z via 3 axis accelerometer.
This makes 6 axis of positional information.
I have a serious issue in claiming a compass has another 3 axis of usable inputs. To begin with, a compass only has 2 axis and only provides orientation with respect to the earth. I can only see this as providing a reference point to a direction in 3-D space no matter the orientation, just as an accelerometer can always tell you where gravity is.
The compass is merely a supplement to the existing 6 axis configuration, it does NOT add 3 more axis (if so, what are they?). 9 input, yes ... 9 axis is merely a marketing term. By that logic, adding a GPS input would make it 12 axis.
Great idea. You could also embed security based upon a persons normal movement to type or move the mouse. Everybody is different, so once you train your system to recognize just you, then anyone else would be instantly identified. You could then have the systems camera take their picture, so you know who tried to hack you.
Just a thought.
One incredibly basic - but extremely useful - feature would be for authentication into a computer. As it is, I work in one location and live in another. Everytime I move my laptop from one place to the other, all of my on-line accounts put me through the authentication interrogation drill before they'll let me in. Cookies don't help. Maybe this could enable a computer to have a "profile for each location". [Or perhaps a programmer could program the on-line financial websites correctly to understand that we are a mobile generation and recognize standard locations for the same user and computer.]