I agree with people who posted in my previous thread that the Kindle has a number of issues (heck, my QuickLink to Plastic.com about this was titled, "Um, the DRM ate my homework?"). But I don't personally expect to use any flavor of Kindle unless I get a grant to test them out or somesuch.
Rather, I see this as being to textbooks what the iPod has been to music. If Amazon learns the right lessons, they can still be a major force in the field, but the important thing is that by proving the concept they'll lead to competitors that will be analogous to the River or Sansa. Once schools get used to the idea of a unified eText delivery system (and I expect several will be roped into multi-year exclusive contracts, but even those will go away eventually), alternatives will appear, DRMing will abate, and once again the guy in XKCD will need to find something else to complain about. ;)