It does change the situation a lot if it's FPS games other than UT and Quake etc. that you're playing. I'd bet that System Shock 2 would be awesome on a cab, as would any of the Jedi Knight games. The Jedi Knight games might even play so well you could built an arcade machine just for them. Trackball, analog joystick w/ 2 or 3 buttons, and a bunch of illuminated buttons in circles around the trackball for force powers. It'd look great.
I don't think you'd need a particularly high resolution trackball to play those games. I think what you do need is a joystick that has at very least a top fire button, if not a button each for fire, alt-fire, and jump. An analog joystick would work well because they have accessible buttons for all the actions you'd need, and it gives you analog control over your walk speed.
I have a first-person game called Gothic installed on my cab, and it plays pretty nicely with the Happ 3" trackball I have in there. I do agree that the 3" would be too heavy for your typical FPS game, which is much faster paced than Gothic is. I think some others to consider would be GTA and Vice City, Jedi Knight games and System Shock 2, the Thief series, and possibly Tomb Raider games (who knows, when played on a cab they might not suck...), and any of the PC role playing games. Except the massively-multiplayer-online-RPG games. Those should never be played, ever, by anyone, unless under duress.
