I have a Kindle DX which I generally like, and for which I have gotten a number of books, but I do have some suggestions:
a)Having now used Kindle on PC and Android phone, the DX interface seems very clunky. Touchscreen please.
b)DX size (10.7") is too big - I should have bought the smaller regular Kindle.
c)Lack of color is is a significant handicap.
d)Still not enough technical books. A number of conversions to Kindle format are flawed, especially of equations.
e)Proprietary restrictions are a pain - Kindle books are not available from libraries, for example, unlike other formats.