Do you experience lag when you turn the pages of a book? Of course you do, unless you're saying the page turns instantly without the page moving. I see no problem with less than a second lag when I turn the pages on my Nook Touch. The screen is small but it's roughly the same size as the average novel.
Originally I didn't want to get the Nook Touch due to its price but since buying it I've read over a thousand pages on it and I absolutely love the thing. In fact it's made reading so much nice that I can't stand reading long pieces of text on my screen anymore, I copy and paste to Libre Office, convert the document to PDF then read it on my Nook.
If you intend to use an ebook reader as text book replacement you are making a huge mistake. There is no way in which one of these can replace traditional books, whether for class or for your own use. It is simply not possible to look up information very quickly dozens of pages from where you are in an ebook, it's not possible to underline or annotate, etc. thus text books are irreplaceable.
Ebook readers are great for reading novels, nothing more, as large or long pages get stretched onto more than one screen, making them unsuitable for academic uses.
Edited by Liranan - 12/20/11 at 7:50am
Princeton did a pilot study with the Kindle a couple of years ago and found it "not conducive to academic purposes".