I got to play with an eInk display today, fresh from Japan. Not the one pictured at engadget, but the same idea.
It's cool. The most apparent thing is how bright the display is and how it looks good from any angle. Passive lighting is a good thing. The redraw rate is horrible and the algorithm is weird: does some sort of inverting of the screen. This all makes this generation of tech useless for most computing applications. But as an ebook, it's good.