Screen size and weight. It feels like holding a (very) light paperback. I had no problems reading on my back for hours, holding the screen over my head (can't say the same for a Steven Erikson hardcover). The print size is adjustable for those with bad eyesight though I kept it at a standard paper-back sized font.
Didn't hurt my eyes one bit. The e-ink technology they use feels to the eyes just like reading a regular book and I don't know if I will ever touch my Kindle for PC application again.
The web browser is more of a pleasant bonus than anything else. As one of those barbarians without a smart phone it will be nice for checking things on wikipedia or reading my daily blogs when I'm someplace without my computer (but with wireless, for I did not get the 3G model for the extra $50).
It can hold MP3s. I'm sure I read this somewhere before buying, but it surprised me anyway. I threw a couple episodes of Writing Excuses on there yesterday but for anyone with an MP3 player this really isn't that fantastic. It doesn't have a lot of memory but will be a good place to keep audio books--if I ever buy one. What it does not have is a navigable menu for your MP3s; simply a press and play.
The web browser goes under this, too. It has a tough time rendering pictures and can be slow and choppy. It has an awkward cursor thing that lets you navigate but is less than functional if you're in a hurry or at all impatient.
The touted free ebook archive we've heard so much about is kinda underwhelming. I'd hoped for something that I could browse during work, plucking this book and that and whisking it to my kindle. Instead I found links to several websites (archive.org, openlibrary.org, and gutenburg.org) not a single one of which I found "browseable." Go ahead and call me lazy. I don't mind. It just didn't live up to my expectations. I'd hoped to have hundreds of awesome old books on my kindle in a few days. I'm up to about sixteen that caught my interest and those were mostly childhood reads (Les Mis, Count of Monte Cristo, etc). If a book is public domain and you know exactly what you want, you will probably find it on one of those sites. But don't expect to jump on the internet and fill your bookshelf. Running down a brightly lit bookstore aisle with a shopping cart and carte-blanche this is not.
The Coolest Thing So Far:
I figured out how to put my own work on the kindle. It's really quite simple once you figure out how to save your files and where to put them. The formatting isn't perfect and I won't be able to effectively edit on the thing. What makes me the most excited is my ability to have a non-editing, comfortable read through of one of my books without having to sit at the computer. I kicked back on the couch and read Drums of War on and off throughout the last day and a half and was delighted.
It gave me a feel for how the book would look on a printed page. It didn't hurt my eyes or back and it didn't feel at all like a chore or work. It felt like I was on my couch reading a paperback. And that alone may be worth getting a kindle.