I tried out the Kindle 3 today at my local Staples. I just loved the speed of the page turning - wonderful. I also liked the K3's Pearl screen.
But I didn't care for the tiny page turn buttons. They are way better than the buttons on the Nook, but I use page swiping almost exclusively and using the K3's buttons seems like a throwback. The keyboard was kind of interesting, though I don't think I'd use it much.
The K3's speed of operation is its biggest advantage over the Nook, in my opinion. I'm waiting to see if the upcoming firmware update for the Nook brings its speed close to that of the K3. Then I'll make up my mind whether to buy a K3.