I would want one, but I can't imagine a better setup for FPS games than a keyboard and gaming mouse. A lot of FPS you need lots of keys to shortcut between guns (I want to push a num and get a gun, not scroll through them with the mouse wheel), use items, strafe, lots of things. And I can't get the same kind of speed and accuracy from a trackball in the ways I need it. For missile command, super - but not for Aliens V Predator 2. Nope. Apparently thats just me though.
Good for you though, if that setup works for you.
And I like that someone's doing it, plenty of newbs used to all the time ask about the best controls for Grand Theft Auto: Vice City, but not one of them can I recall that came back latter and told us how awesome it worked out.
Just the same, this will be an interesting read.