I bought a Nook, Sony prs-900, Kindle 3 and Sony prs-350. The touchscreen and sluggishness of the Nook did bother me, but overall it's still a viable device I'd say. It was a little heavy, but for my hands it was a nice size, nothing really bothered me about it physically. For just reading, it was fine. Where it annoyed the heck out of me was whenever I had to navigate thru the touch screen for anything...completely slow and unresponsive.
The K3 is also a great device. It's interface is completely unique, but overall I'm satisfied with it...and honestly, what I like about the K3 the most is how responsive it is compared to the other readers I've owned. What I dislike the most about it is the idea that Amazon can snoop at anything I load onto the device.
The Sony 900 was a great device, I only returned it because I'm waiting for the 950.
The surprise in the bunch has been the Sony 350. I thought I wouldn't care that much for it, but it's become my favorite reader because of it's light weight and small size. It literally will fit in the front pocket of my pants. The screen on the 350 and the K3 is beautiful, very easy to read with a slight edge to the Sony for their nicer serif font. I'm not a fan of the K3's fonts. Also PDF reflow on the Sony works really well...something the K3 doesn't have...on the other hand the Sony has no wifi or 3G..
Anyway, I'm probably sticking with the K3 and the Sony 350 for the time being.... For me, there is no perfect reader yet..Oh, the Nook is being given to a friend of mine..