What rocked to me was the interaction between both displays..., that is, linking all the relevant information and hypertexts which are availabe in the web (next to your eyes, next to your book, a whole world of information to be integrated...), with just one click, embedded into your document... is the epitome of annotation!!!
It's annotation taken to a higher level. It is "digital hyper-annotation", and intersemiotically too, because you not only add links, but handwritten graphics, annotations, gestures and signs, personal codes, underlining, highlighting.... You cannot do ALL this unless you do it this way; you cannot go to a library, cross check every name a document contains, look for additional side information and put each ramification of data it into a printed book. If you collect all the side information, you would need a truck to carry a thousand books.

So, summarizing, as I have said in other post, with the 2-display integration, you fit the internet INTO your books and you turn a simple document into a knowledge base...

Other thing which impressed me very favorably was the "sturdiness". I have had my Palm displays broken or cracked in the past, and know firsthand how vulnerable "tablet-like" devices are. The Edge seemed to me to be a solid, resistant, reliable device with its clamshell design. I agree with Boris, it's conceptually like a book, but does not feel fragile or exposed.
The representation was "This is not a toy", this is a real thing.