Summary: If you have a mac, the driver for the space navigator doesn't work. It works the first time you install, but the next time you reboot, it doesn't seem to work. The only way to get it to work is you have to reinstall the driver every time you start your computer. what a pain. until they fix this, stay away. When it works, it is a good 3D mouse.
Summary: Well, I certainly don't find this input device very usable. Even after a short time of playing with various programs like Google Earth and SecondLife my hand starts hurting. The problem is mainly that software designers like those at Google demand that in order to use the thing to fly very slowly over a city, your hand needs to constantly press the knob in the lateral direction, where there is the most resistance.
Summary: This is a really great product which i would have loved to use, but it didn't seem to work very well on my mac. In SketchUp it seemed to have flaky performance, and i couldn't for the life of me figure out how to change any settings for it. In blender it just didn't work at all. High quality hardware, low quality support.