That looks like an awesome idea, but there's just one problem I can see with it.
Let's say you're playing a FPS on that bad boy... You start to run with your character, and then stop at a corner or something... If you were to do this in real life, your body would balance you in such a way that you could quickly decelerate and still be vertical. On this machine though, you would get the ball rolling at a speed, then when you attempt to stop on a dime, the ball would keep rolling, sending you arse over tea-kettle in the process....
I always imagined that the product that would work best for this sort of thing would be more like a circular convex-shaped treadmill. It would have rollers on all sides to allow it to move in whatever direction... And of course, you'd look less like a hamster.

- FA