Agreed, while graphics look pretty good in my opinion (compare it to an old black- and white television, if you have been there) the screen is too small for unscalable images - you'll want more overview than a 6" device can give you. I would say 8" at the very least in landscape mode, or better yet, a 10.2" device like the
IRex Digital Reader.
Beware of the pricetag on those though, the main reason I still went for the PRS-600 despite wanting to use it for textbooks also.