There is a phosphorescent (same shit that makes your watch hands glow in the dark for you non-chemists) compound put into the surface of the mouse pad, probably specifically tuned to the wavelength of the red laser that 99% of optical mouses use. As the mouse moves over the surface, the laser charges the phosphorescent compound to glow. Bam, Tron mouse.
Yeah that new movie looks kinda really awesome, as for how the mouse pad works I kind of understand; I wouldn't be able to put any of it into practice though =S