I have a nook and I love it, although I have to admit that I wish the battery life was longer. It doesn't sound like my battery life is as bad as Sarahsbloke, but it certainly is much less than my Sony 505.
Anyway, a lady I work with just got a K3 delivered yesterday, and I must say the screen on it is very nice. The K3 is very light weight as well--but the actual size of the reader (Length and Width anyway) was very comparable to my Kindle.
I'd still choose my nook over the K3 though--mostly because I really enjoy being able to download books from the library. I think I prefer the LCD touchscreen of the nook over the K3's keyboard, although to be fair except for a very limited time playing with it yesterday, I've never used the Kindle's keyboard interface.
I am very tempted by the new Sonys though. My husband has a Sony 900 and I love the way the touchscreen interface works. If it's true that they have indeed made the screens on the new models much clearer, I'm going to be severely tempted to buy a 650. I don't need wifi and I really like the way the Sony has integrated their dictionaries.
dordale