Anxiety of Influence
Kristin Lucas, mousepad drawings.
Lucas inked a mouseball and let it make gestural drawings while she played games, answered email, etc.
Eyebeam Open Lab - mousepad paintings
Similar gesture paintings made with a USB "double mouse"
(hat tip to jim bassett--demoted from "attack of the clones" to "anxiety of influence" since the Lucas was part meat-space, part virtual and the double mouse is all virtual. it is basically the same idea, though)
Update: another mouse doing "automatic writing," by Joseph DeLappe, from '99 (thx to ed halter)
Update 2: Some critical musings on all this are here.
my ex girlfriend also did this exact project a couple years ago for a class (no link, but looks the same as these)
There's also Claude Closky's Mouse Works: closky.downloads.online.fr/wallpaper/