If you were a student (or if you are a student) would you buy a $500 Kindle to read textbooks, plus a lot more to download digital versions of the texts? Unless there's a slam-dunk cost benefit that students can see, I don't think this is going to make a huge impact on the textbook market at this price point.
As for magazines and newspapers, I don't think most people can justify a $500 expense to read magazines and papers that they can get for much cheaper in print or free on the Web. I subscribe to the WSJ for $90 a year and read the NYT for free on my iPod Touch and Web browser. Even if the NYT started charging $50 for the Touch and Web versions, it would still be just a fraction of the investment required for reading it on the Kindle.