Trackballs really aren't _that_ terrible for precision in FPS. Not pro level, but heckuva lot better than the joystick control consoles currently use. I found I had a harder time in StarCraft than I did in UT2K4, but both were quite playable.

I used a Logitech Trackman for seven years, and the biggest issue was that the force required to move the ball around wasn't constant; it would vary depending on how gunked up the little rollers inside had gotten. I had to clean mine out every day to keep it smooth.

If a person prefers using a trackball, that's great, but when the same tools used by the pros costs about $50, there isn't really any other reason to use anything else.