At the heart of the SpacePilot PRO is its support for 3D applications, whether its 3DS Max or Maya. The mouse can actually move in all three dimensions (X,Y,Z) simultaneously, using 3Dconnexion's "six-degrees-of-freedom" technology. By lifting, pressing, and turning the controller cap, designers can easily pan, zoom and rotate without stopping to select commands.
I'm sure some 3d designers will use it just for that. I know I would. 500 is not a massive amount if you consider it from a workstation point of view. If something like this will improve your productivity then I'm sure you'll consider buying it.
From a home consumers point of view its defo expensive and mostly useless.