There was a similar project that used a microphone affixed to the table that would detect and measure the change in pitch as the user scratched or tapped the surface. It had the advantage that the user could place their hand anywhere on a desk, so they were not constrained to a particular location like this infrared solution. I wonder what the resolution of either of them would be. Probably good enough to demo but frustrating to use in practice would be my guess.
> -----Original Message-----
> From: email@example.com [mailto:firstname.lastname@example.org] On Behalf Of
> Erico Fernandes Fileno
> Sent: Monday, June 21, 2010 10:15 AM
> To: Mila, Brian
> Subject: Re: [IxDA] Is the mouse dead?
> This project of MIT it's a good way to think about mouseless...
> http://www.pranavmistry.com/projects/mouseless/ 
> It's the same mental model of interaction with a mouse, but it's good
> think our relationship with objects.
> Fernandes Fileno, M.Sc.
> Senior Interaction Designer @ CESAR 
> Curitiba - Interaction Design Association
> On Mon, Jun 21, 2010 at 9:09 AM, Brian Pirie
> >While I don't think the mouse is dead, nor will be any time soon, I
> >that's missing the big point: The days in which the mouse was the
> >pointing device are long gone. When you consider the predominance of
> >with touchpads, the rapid rise of touch-interface devices like phones,
> >iPads, touch-enabled computers, and less common devices like Wacom
> >the mouse is no longer king.
> >This means that designing a web application or other product that will
> >used on multiple devices, assuming the user has a mouse, is a recipe
> >failure. The implications range from the obvious like avoiding words
> >"click" and "mouse", to the far more subtle but significant, like not
> >relying on mouse hover behaviour, and not making hit areas too small
> >reliable touch with the finger.
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>  http://www.pranavmistry.com/projects/mouseless/
>  http://www.cesar.org.br
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