I have not got a kindie. I looked int eh Kindle in some areas the books available are seriously limited. In many cases there are substitutes but the authoritative reference is not available, so if you want Garey and Johnson they you are out of luck. The cost of these books make a kindle look much more expensive.
I suspect many of the fundamental source books will never become available in PDF format.
It also would be nice to have a way to oragnise and carry around large volumes of articles extracted from electronic journals. You can theoretically buy these but the only sane thing is to use an academic library's subscription. Those without access themselves should button hole a friendly academic.