I read almost twice as many books since I got my kindle for Christmas last year. I even prefer reading on the kindle to reading on a pc/tablet or a traditional book.
That said, for reference books, it's worse than the alternatives. I almost exclusively use it for reading books back-to-back (i.e. relying very little on the arrow keys)
I've found that a 10" tablet (a Touchpad in my case, though I imagine the experience with an iPad is equivalent) it pretty tough to beat for reference material. Doesn't have the navigation issues that the eink readers do, but it also allows me to make searchable annotations and highlights as I read.
That said, for reference books, it's worse than the alternatives. I almost exclusively use it for reading books back-to-back (i.e. relying very little on the arrow keys)