I'm not sure how well that works, though. Ebook readers take about a half a second to refresh the screen, it's not done several dozen times a second like on a standard screen. It refreshes localized areas a little faster, but it's still quite laggy as far as input. For now, readers are better suited to reading than highlighting, underlining, notetaking, etc.

As far as textbooks, most e-readers have the capability to re-flow pdfs. The technology works pretty badly with images, though, and images (graphs, figures, etc) are an important part of textbooks. If you think of your average busy textbook page, and then think of a small screen trying to figure out how to re-format it to look better, well, you can imagine there are problems.

With that said, on the new, bigger Kindle (the DX) pdfs should look fine looking at the whole thing on one page. Suppoesdly, the DX is a very good option for texbooks, professional documents, etc. Unfortunately, it's a little more unwieldy for personal reading as a result.