Steam controller development looked pretty rough.

[RainMotorsports]

Valve Controller Prototypes

One of the first was apparently a Xbox 360 controller hacked to hell:


Looking through the gallery they not only wanted to try out a track ball one of the models had the ball accessible on both sides.

 

[HeatSurge]

I had a trackball. Played RTS with it but not FPS, not competitively (single player only). I've been entertaining some thought about getting one again, it was nice, but it got dirty and it didn't feel as nice after a while :-( ...