The E-Ink displays also use a lot of power at reasonable reading rates, like one Swindle screen update per minute seems to use about 100 mW. That's about three orders of magnitude more than the 2.7" memory LCD, which I guess is about an order of magnitude less area, so it's about two orders of magnitude more power per area. But the memory LCD updates at nominally 20 Hz and potentially much faster, so it's three orders of magnitude faster, so in some sense it's five orders of magnitude better than E-Ink.

I have seen a Swindle do partial screen updates much faster than 1000 ms. In fact, I originally wrote http://canonical.org/~kragen/sw/inexorable-misc/tetris.html to play in the browser on a Swindle, with update times of more like 100 ms. And I successfully used IRC on it, too.

The E-Ink display does have some good points: it's not glossy, it's available in bigger sizes, its whites are whiter, and it can do grayscale. But, for interactive computing, I think those aren't a good tradeoff for being orders of magnitude worse at power consumption and update times.