Yea, I thought about doing UT on a MAME cab and it would be kinda hard.  Sure, a 3" trackball is an excellent turn left/right, look up/down control.  Sure, a joystick would be awesome for running forward, back and strafing left and right...
That's two hands taken up already... next / prev weapon, primary / alt fire , jump / crouch take an extra 6 buttons.  Where you're missing are the mouse buttons and scroll wheel.  Without those, things get too tough.
...Unless you're a mutant with three arms. 
