I've used a 3DConnexion "SpaceExplorer" spaceball (USB interface, forget wireless) forever, both at work and with my own laptop for running/teaching Inventor. With the spaceball in my left hand and a 3-button mouse in the right, I can zoom and rotate the part/assembly much quicker and more accurately while selecting features with the mouse. I find that having the wrist rest attached allows me to more accurately move the image (unlike the SpaceNavigator, which has no extension).
Yes, spaceballs are expensive (mine was free from work
), but I swear by them, and I highly encourage all of my students to get one (or something similar) if they plan on getting serious with CAD--makes working in 3D so much easier. They are always fascinated when I pull out the spaceball and show them how to use it...plus, they get jealous after seeing how fast I can maneuver.