When I first started using a Mac in 1995, my finger working the mouse began to hurt after a few months. As a designer using Photoshop, InDesign, Freehand, etc, I scroll a LOT working different palettes or drawing logo shapes. The last thing I wanted was some type of "work place" disability. I finally went to an Orbit trackball. I'm on my second one now. It's perfect... can scroll quickly, fingers don't hurt, saves desk space, etc. Even my wife switched to one.
I use the pad with my fingers on my iBook when I'm out of town, but it doesn't come close.
So, I'm not using Lion yet, but I hope trackballs are here to stay for designers... until some retinal focused laser guided scrolling system gets implanted in my head!!