How well will this work in practice

The startup's site is advertising preorders at a cost of $70, expected to ship in December 2012 or January 2013. From their about page

Leap represents an entirely new way to interact with your computers. It’s more accurate than a mouse, as reliable as a keyboard and more sensitive than a touchscreen. For the first time, you can control a computer in three dimensions with your natural hand and finger movements.

This isn’t a game system that roughly maps your hand movements. The Leap technology is 200 times more accurate than anything else on the market — at any price point. Just about the size of a flash drive, the Leap can distinguish your individual fingers and track your movements down to a 1/100th of a millimeter.

That's a pretty impressive accuracy claim. Now the question is just how well it actually works. (If you qualify, they seem to have some free developer kits which are estimated to ship in 1-3 months. Human-computer interaction isn't really my area though).