Leif and I have had our Kindle 2s for all of 24 hours, so this is my initial take on it.
1) The "screen" is much better than you'd think. It literally looks like a piece of paper (the best piece of paper you've ever seen). I'm not sure how they do it, but it's amazing looking. The fact that you can change font sizes easily is great, and the "look this word up if you don't know it instantly" is really good as well.
2) It's very very comfy to lay in bed and read it, especially with the "next page" buttons on either side. You can have 1 hand petting the dog, and read with the other without worrying about losing your place.
3) Downloading books is extremely fast.
4) I tried the 14 day trial of Newsweek since I get a paper subscription. It's ok, I'm not sure if I'm going to cancel my print subscription though since there are some articles missing. Basically anything with big charts or something instead of just pulling out the charts, they pull out the article.
5) If you and your spouse each get one, you both can read the same books, but not the same magazine or newspaper subscriptions. So it's good and bad. The latter is annoying though since if I'm done reading a magazine I can just hand it over to Leif, but in bizarro-DRM world, you can't do that on the Kindle. But there is some measure of comfort that if I buy a book for $9.99 we both can read it.
6) It's very responsive to changing pages. The screen flashes when it turns a page which is a little annoying, but you get used to it. It's kind of nice to have some sort of feedback.
7) Getting book samples is very nice - I downloaded a few last night.
8) There are a TON of sites with free ebooks (like stuff in the public domain) that easily convert to Kindle format. Random House also just did a promo where they released 8 books free (I guess those authors had new books coming out). I downloaded all of them (all were in Kindle format), and the majority of reviews on Amazon were 4 or 5 stars.
9) It will be much nicer to take this on vacation instead of carrying several books with me. I'm going to Cozumel at the end of March and I'm most likely going to buy a few books I've been wanting to read and just take the Kindle instead of loading up my carryon. Depending on the trip, I can go through 2 books at least (last year in Bahamas when I was sick, I read 3 since I couldn't dive, and ended up switching books towards the end with someone else on the trip).
10) Well that would be a downside I guess, what I just said - you can't just switch books with someone if you want to unless they're also on your Kindle account.
I'm actually much much more impressed with it than I thought I'd be. The absolute biggest downside for me right now is that I have a few print books at home that I want to read, and I don't want to re-buy them in Kindle format. I wish Amazon would have some sort of discount, like if you bought the print book from them, you get the digital version either free or at a reduced price. Kind of like what Disney is doing now with DVDs - I've noticed that if you buy a Disney DVD now (maybe not on all of them, but on a bunch), you automatically get the digital version.