What a tablet computer can be:
(possible forecasts for the Apple tablet)
1. Have an aspect ration of the 'Golden Ratio' Phi (φ) 1.618. Possible resolution of screen (under the commercial availability as of Jan 2010) 1280x800 or 1280x768 (or perhaps even 1440x900.) About 10 inches diagonal.
2. Have a finger and gesture touch interface. No pointer on the screen. Designed to function with fingers, not stylous.
3. Have more 3D (real or 3d-looking) user interface elements, like coverflow and the date-time picker found previously on the iPhone OS. 3D looking home page(s.)
4. Runs on arm cpu and has 3D acceleration.
5. Has webcam.