I always wanted working from a tree
I see that people are pointing out that you won't be able to see videos, animations etc... For me that's a big advantage!
It is easy to procrastinate when programming, e.g. when you wait for some computation to finish. Now with E-ink screen you cannot watch flashy websites like youtube, facebook (pictures will be distorted too much, and let's face it, people use fb to spy on other people, that's a fact
) etc. you concentrate on work.
This fact alone would increase my productivity by tens of minutes a day, which for some people (e.g. students) might be the no.1 reason to buy such device.