Update: We just got some more time with a functional unit, and while we aren't allowed to use it, we can say the build quality is sturdy, there's a good rubber backing, and the viewing angles are quite nice. It's crisp, too, the screen, although page turning is somewhat sluggish, the software perhaps not finished. Article view is a nice touch, being able to read just the piece formatting-free -- and you can skim through the articles alone by swiping to the left and right. You want some more shots of the UI in action? You know where to look.
Update 2: Well, that was tough! We finally got some "alone time" with the Nook Color, although we still weren't allow to put our apparently grimy fingers on it. You can check it out in the video below, but we still seem to think there's some software tweaking going on as it's a bit sluggish to switch through menus. While we're still of the mind that this device should have had a PixelQi or Mirasol display, we can report that the LCD is responsive to finger swipes and the viewing angles are quite good (believe us, we were looking at this thing from all angles as book-loving journalists swarmed it.) We can't and won't make a final call on the Color until we get one into our hands, but the video below should give you a better idea of the UI and performance until then.
Working Nook Color hands-on
Nook Color mockup hands-on!