I have often wondered if the choice of SIZE of display of a digital assistant (mobile phone, netbook, laptop, desktop, etc) is determined by whether you are long or short sighted. Seeing friends struggling to read menus or hunting around for their magnifying spectacles to use a small screwdriver reminds me that we all do not see the world in the same way.
Being short sighted means that mobile phone and small screen laptops are easy. Yet, even with this facility, the amount of space, just space, for seeing the "complete picture" is missing. I need to read more than just a few characters of text.
So, this is where the i-Pad will be a hit, I think. A big enough display to see what you need. And coupled with the i-Book you have great possibilities.