Developed at HP Labs (now spun into Agilent), manufactured as a small single chip solution which is then sold and repackaged by other manufacturers (Microsoft, soon Logitech). Word from the inside is that the idea is a derivative from handheld scanning research (waving a handscanner over a page which would then be reconstructed on the pc). It looks, smells, and tastes like optical flow which is hardly something they could claim as their own invention.