(I don't own the actual Kindle gadget, so I don't know how much it may vary from the iPhone's version.)
1. The application is free to download! (Though the actual books cost money - how dare they?)
2. I can read at night in bed without turning on the lights and consequently disturbing The Doomed.
3. You can download free samples of any book Amazon has available electronically. (GREAT for deciding if you really want to spend $9 on a novel you can't place on your bookshelf.)
4. You can buy books right from your phone (either through the Amazon application or just using your web browser) and they zoom over to your phone in less than a minute. (Although this is sort of awful for my tendency towards impulse-purchasing - yet another reason to love the free samples!)
5. Not all, but a lot of the books still include any pictures that come with the actual physical books. (I read a lot of biographies and those usually have a few pages reserved in the center for relevant photos - I like that.)
6. You can highlight text, tab pages, write notes, and look up the definition of words - right on the same page you are reading.
7. Books vary in prices, from free - about $15.00, so everyone can find something affordable.
8. So handy to read anytime you want. (Who doesn't always have their phone handy on them anyway?)
(Disclosure: I am not associated with Amazon, Apple, or the Kindle device in anyway and have not received any compensation for the above review. I'm just a fan of my gadgets. :) )