I reckon this whole scene will change in 1-2 years' time, with devices such as
this with a hopefully much improved display re-writing speed, enabling a moving map GPS to be implemented.
Current e-book readers such as
this (I have one of those) cannot do that because screen rewrite is extremely slow (or so it seems; there may be a way to re-write just a small piece of the screen, but Irex won't talk about it).
The e-book readers are so much lighter, thinner, less power hungry, that they will pull the rug out from all the current aviation GPS products, IMHO.