Why would you waste your time getting a pc trackball, when you can buy real one's pretty cheaply? The arcade trackballs are way better then using any type of pc trackball.
I really didn't find it a "waste of time". I bought a clear PC trackball from compusa about 5 years ago and it worked like a charm (sorry can't remember the actual name or model). Mounting from underneath was easy enough and the interface to the PC was obviously plug-n-play.
I play marble madness, golden tee (older versions), centipede, and missle comand well enough with it. I even play arkanoid and tempest with it - took a little training, but they play fine. And I have scored a couple 300s on Capcom Bowling.

For all games mentioned, I think I only had to tweak the settings for golden tee and arkanoid.
I am by no means a junky with those games; and I'm only running version .60 or so (I could get the actual version number if its important to anyone), but I thought it worth to point out that someone has had some success with a $15 PC trackball.
With that said, I am probably the only one to really play the trackball games; kids are too young and friends only interested in joystick classics. I do believe that a real trackball is in order for rugged play. And given that they are much more available with USB I believe the extra $$$ is worth it.
--JamIt