I dropped by Best Buy yesterday and picked up one of their cheapest Logitech optical mice (CDN$14.99+tax).

I opened it up today and sure enough, it's using an Agilent ADNS-2501 sensor. It's in a DIP package (yes, the pins along each side are offset by 0.05" as shown in the datasheet), has quadrature outputs, an SPI, and if you look on page 33-34 of the datasheet it can dump out the 16x16 pixel image it's "seeing".

In short, with the right optics you have a single, low-power chip that can see 2D motion and capture images to pass up the processing chain. Get two and you could have some very interesting stereoscopic motion control potential.

It's a hackcident just waiting to happen!