...why use 90 markers?

I saw a demo a while ago where they used Infrared makeup on someone, and used a sponge to make it really splotchy. The makeup doesn't show up in Red, Green, Blue wavelengths.

So, they could simultaneously capture RGB, and IR. Using multiple cameras on the IR, and the splotchy makeup, they were able to capture thousands and thousands of points, and get color info at the same time.

Seems like the right approach to me. I could totally see a Kinnect-like device taking advantage of this, allowing someone to do facial capture like this at home.