Starting last night and finishing during my free periods today, I decided to test run the readability of an entire book on the iPad in the iBooks app, Apple's ebook store. I downloaded The Time Machine to be my test subject since it was free and it is has been on my very long list of things that I just had never got around to reading.
For the most part, despite the nice look of the double facing page view while in landscape mode, I think that I prefer reading in portrait mode with just one page visible at a time. I read in my living room while in my awesome Ikea chair, in bed with both my side lamp on and off, and in the teacher's lounge while under the bright fluorescent lights. In all those different lighting conditions I did not find myself feeling any noticeable difference while working through the novel. The text at the stock setting was very easy to read, even without my glasses on. When I use my laptop in bed, I find it hard to read text from websites, docs or just about anything without them. With the iPad, I had absolutely no issues reading, just like I would a normal boo without my glasses/contacts.
At the end of all my reading sessions, I didn't seem to experience any eye fatigue or headaches even though this is very much a computer-like screen. As far as that argument for the eink on the Kindle, for me anyway, the screen on the iPad seems to be just fine.
As I showed off the iPad today to some colleagues, the initial reaction to the iBooks app was almost universal: image giving a student an iPad loaded with their course books for the year. Between the rich color, ease of access, long battery life, built in dictionary, and numerous other things, I don't blame them for their bit of drool just thinking the possibilities. If Apple works on making a lower cost version of the iPad for edu use and the textbook industry finds some common sense to charge less for a digital version, rather than the print, some amazing things could happen in the edu arena.
Couple quick access to all their books with the built in web and collaborative tools and suddenly things get mighty interesting in the classroom. We aren't there yet, and you would need universal access to wifi throughout the school to really make it work, but we're getting there.