|^ Yeah, but drawing with your thumb (or middle finger, depending on the type of trackball) is kinda... weird.|
I draw from the wrist/elbow/forearm, like most people.
Also, it is good that trackballs are popular for CAD, but CAD drawing in its most typical form (making plans of buildings, mechanical parts, etc) is a lot different from freehand drawing. Typical CAD is more like putting vertices in coordinates in space and then having the program connect those vertices.
Freehand CAD is a different story. I am sure you can do it from your thumb using a trackball, but I believe getting the hang of it is gonna be a rather long process.
However, I may get myself a trackball eventually. I guess it would offer some comfort, at least for browsing.
And wow, those trackballs tend to be expensive.