I bought a Kindle a few years ago and what I found most useful with it was not what I had first expected. I have always been an avid reader, fact and fiction in equal amounts. A key component for being able to read a lot is of course to be able to read fast. Being able to read fast (while still comprehending what you read) is immensely useful. Many people never learn past the one-word-at-a-time-technique which is a shame since increasing your reading speed is quite easy.
Although it might feel like it, reading is not done in a linear way but rather in a sequence of jumps where you fixate on parts of the text in each jump. So basically, to read faster you want to minimize the number and durations of fixations per line. In the “worst case” you will fixate on every word in a line. But with some training you can increase the peripheral vision registering more words per fixation, thus increasing your speed. In a standard book or text the lines are usually so long that you need several fixations for each lines. But if the lines are short enough so our peripheral vision can register the whole line, we can virtually eliminate the need for any horizontal jumps and instead let the eyes travel in a vertical line along the middle of the text.
And with the Kindle, this is very easy to set up. The Kindle has two settings that can control the length of each line; the font and margin size. By increasing the font and margin size the length of each line will become shorter. This makes it easy to find a length that you feel comfortable with.
One thing I do lack in the Kindle is a tracking guide that helps guide the eyes down the lines. A common way of doing this with an ordinary book is to use a pen to track the lines while you are reading. I have never been very fond of this myself but some sort of visual cue would probably be useful. Perhaps if the middle word was bold or in a different color it would be easier to keep the flow going.
If you are interested in learning more about speed reading techniques, this is a good starting guide: http://fourhourworkweek.com/2009/07/30/speed-reading-and-accelerated-learning/