Trackball is the same idea. Hold an old ball mouse upside down and you have a trackball.
Old ball mouse? What is this ancient and mystical technology you're referring to? It's long forgotten!
Hehe ok, you're not
that old
It is the same idea, but at least the trackball is geared for that so rolling it is not as awkward.
I would really love to try a gamepad with a trackball for instead of a right stick, at least just to see what it's like.
By the way, I've been looking into it and apparently there is a mouse for the PS3 that is basically recognized by most games. The problem is that games made for consoles are not built to recognize a mouse at all (except UT3), this mouse apparently tries to work around that by registering as the right analogue stick. You have to configure it for each game to get a good feel of it but it seems like decent product.