If I read a book I constantly jump to the same line. With adjusted fonts, font size, line spacing I do not have these issues. My kindle is jailbroken and runs KOreader. Even more funny the lowest brightness setting 0 would still have backlight on (stock FW - Kindle PW3). This isn't the case anymore. I read in bed on the sides and nothing is more annoying than a big book to hold.

If I want to read fast I prefer one word on the screen at 250-450 words per minute.