To all the people not agreeing that a trackball isn't as precise as a mouse for FPS games is mistaken. It's actually more precise than you think, but yes, it does take a little bit of training.
The last LAN I went to, was the Showdown LAN in San Jose, CA about 4 years ago. I just happened to be right next to a person that was using a Logitech Trackman Optical. He said it was the best pointing device he has ever used. He was owning people left and right, and even showed me what his 180s looked like and it was pretty damn fast, split-second. Could be wrong, but I actually want to say this guy had carpal tunnel in both his wrists when I was talking to him, he told me. (he had wrist guards on both his wrists) But he was able to use the Trackball with no discomfort.
Also, my neighbor has the older, wired version of this trackball, and can say it's actually a joy to use, even though it's thumb-operated.
Just remember people, this is how the "mouse" started out (to an extent). With the ball on the outside, moving it with ALL your fingers. And if you ask me, using all your fingers, in theory, WOULD be more precise moving your cursor around, than just your wrist. You have to lift your hand off the surface to move forward and backward (on a large resolution display) unlike a trackball that can move in any direction while the device itself is stationary.