1. Send a Sample - instantly sends about a chapter of the book to your Kindle so you can get a feel for whether or not you will like it. Then if you want to buy, one click sends it to your eReader in about 10 seconds.
2. No one can tell what you are reading from the cover. The ultimate in stealth reading.
3. Whispernet wireless download means no more late night trips to the bookstore to fish through what they happen to have on the shelves. Or worse - trying to find a decent book at the grocery store.
4. The eInk display does not give eyestrain. I do not like doing serious reading on a backlit screen. I frequently have to read technical admin guides offered in pdf format for my work. Since I have trouble reading that level of detail onscreen I used to print them out. Some of them are huge - 300 plus pages. Now I can put my work pdfs on the Kindle and not have to print them out just to read through a technical manual once. Saves paper.
5. Knitting patterns work pretty well on the Kindle, as well. Very handy.
6. I don't have to fight to have a paperback lay flat. My M-Edge leather cover not only lays perfectly flat, but it also can stand itself up easel style for hands free reading.
7. The dictionary lookup feature is surprisingly cool, especially when reading the classics and historical fiction. For example, Georgette Heyer uses a lot of Regency period "slang" and I love the way I can just click on a word and the definition shows up on the bottom of the screen.
8. There are lots of free books available. I love the Project Gutenberg "Magic Catalog" where you can instantly download classics over Whispernet. Also feedbooks.com which has a great interface for downloading all different free eBook formats for whatever reader you happen to have. I love that authors and publishers are offering some books for free as well. On Sci Fi Jungle I have a nice list of resources for Free Kindle Books with links, by the way.
9. Lots of new books to buy. The main reason I decided on a Kindle is that Amazon has the largest selection of eBooks available right now. I am sure that the Apple store and Barnes and Noble will be working hard to catch up, but I went with the leader. Plus I love Amazon anyway. Not only do I own a little bit of Amazon stock, but I also make a modest few dollars a month on affiliate sales through them. (Mostly due to their best price on Keurig K-Cups, but that's a whole other story) I am a voracious reader and have books factored into my budget. While I do borrow from the library and skulk around used books stores, garage sales and Goodwill for books, I also buy books new. For my favorite authors I will even shell out for hardcover. I like that there is even a slightly lower price for the Kindle version, although I with the price battles going on right now I am not sure how the price thing will all shake out.
10. Fantastic battery life. If you have to have yet another electronic device, its great to not have to worry about it running out of battery all the darn time. The Kindle has a great battery life which is great when you want to carry it around everywhere you go!