I'm assuming that's what Joe Murray was using to draw Rocko, Heffer, Filburt, and the Big Heads on the special features of Season Two of Rocko on DVD, since he was drawing onto the computer screen, as opposed to using one of those drawing tablets.
I don't know, all those digital drawing tools are apparently not as easy as they look... I recall in one of my old Flash Animation classes, one girl was getting really frustrated because she couldn't get the hang of using the drawing tablet... this light pen thing, assuming it's the same thing I'm thinking of, seems easier and better to use... personally though, I'm old-fashioned, I still prefer to draw by hand, then color digitally.