I wrote a blog entry about the concept of multi-touch mice vs. multi-touch trackpads.
"I can envision an ecosystem where multi-touch mice being accepted as a low-cost enabling technology that introduces people to Natural User Interfaces without a large investment. Those would be used in addition to or to complement multi-touch displays and larger Surface devices. It would benefit NUI adoption by allowing existing computers to use NUI software. While it would add to the complexity of planning interfaces across a larger variety of hardware capabilities, the potential for mass adoption may be more important."