The trouble with the eBook is that it's (relatively) expensive and non-mobile. The G4 power is way more than schools need most of the time. I forsee it being as a higher end computer lab computer for doing the fancy and computationally-intensive multimedia stuff like digital photography, video, and layout. This could be complemented by a more day-to-day useful eBook which is:
*very portable - thin and light, but with reasonable screen space and very good screen quality (because it will be used a lot).
*A touchscreen, so that it requires no keyboard, although one can be wirelessly networked via bluetooth.
*very cheap - no more than $700, and sold in bulk
*very durable with long battery life
*sufficiently powerful to handle essential productivity apps, eTextbooks (as PDFs), basic image editing and drawing, and digital video playback. 10gb of local storage on a mini-drive should be sufficient.
*wirelessly networked, very secure. Hacking should be impossible, and theft should be made undesirable and trackable if possible. Vandalism must be prevented somehow. Student use is limited, er guided.
*Directly controlable by the teacher via a special education edition of Desktop Manager. Can be centrally commandeered to display particular materials, and for giving tests (which can be instantly graded, recorded, and analyzed and remotely observed).
*Handles many basic classroom tasks automatically. Datebook actively reminds students of assignments (and other stuff from the syllabus), which they complete on the eBook, which also records how and when they work, which allows teachers to observe and teach good study habits and avoid plagarism. Students/Parents have access to their (extensive) records. Higher-ups (principals and even district supervisors and above) also have access to full records and analysis, and can remotely observe use.
*Is built with a digital library of resources available on-disk or over the wireless network, including dictionaries, encyclopedias, eTextbooks, self-guided study materials, and so forth. Includes productivity apps like calculators and datebooks. Built in spelling, pronunciation, grammar, and typing (and maybe penmanship?) programs analyze ability and actively instruct as necessary.
Sort of an uber-PDA with teacher control. Naturally, a lot of the software would need to be developed and a lot of digital library resources would have to be integrated. But for a truly useful educational computer, this is essential. Otherwise it's just an expensive toy.