I really got used to a space mouse with a piece of software called Geomagic Wrap, which we were using to take point clouds from a 3D scanner and turn them into solid models. Part of that process involves turning the model every which way to look for holes and whatnot in it to correct, and being able to use both hands for this really sped up the process. At this point I just cannot stand doing the Click-a click-a click-a click-a required to move a model around with the mouse. And if I'm modeling something large like a building or a landscape in a video game? Forget it. I want to be able to fly the camera around.