I'm running 3DxWare 10 Beta 6 with a SpaceNavigator on OS X 10.8, and the latest version of Sketchup (8.0.15157, downloaded about a week ago). I get erratic startup behavior. If I start Sketchup after a reboot, the Space Navigator does nothing. If I close Sketchup, and reopen, it sometimes works, sometimes not. If I close Sketchup, run one of the 3D demos, then start Sketchup, it works.
Also, with the latest version, Sketchup freezes on me at least once a day--usually after a period of inactivity. I've also had several crashes. Not sure if this is caused by Sketchup, or the 3DxWare.