I would see if your library uses Overdirve or another source for ebooks and audiobooks, and what formats they have available. I didn't think I'd use my Nook for library books, but it is great for books I'm not sure if I want to buy.
I believe both B&N and Amazon sell textbooks, so you should be covered there. You would probably want to take notes then if you use your reader for school. Do you think a physical keypad or touch screen would be preferable? I would go to B&N and play with the Nook a lot. Take notes and highlights, see if it's to your liking. When the K3 comes in you can try out the same thing on it (or use the Kindle 2 for now).
Also, I listen to audiobooks. You may change your mind someday. They are great while exercising, cleaning, driving etc... Both Kindle and Nook play them, but Kindle supports Audible (which a lot of people don't use). I don't use my Nook for audiobooks though, I love my phone for that.
From the sounds of it so far, you would probably be happy with either device.
