Microsoft CEO Steve Ballmer demonstrated Windows 7 running on a prototype HP Tablet computer (referred to as a "slate") at CES 2009. This was used to show the Amazon Kindle for PC e-Book reader software. What stuck me about the demonstration was how clumsy the device was to use . With a screen of about 10 inches screen, the device is too large to hold comfortably in one had and operate with the other. The unit in Mr. Ballmer's hand is wobbling as he operates it. This is too cumbersome for a usable e-Book. As suggested previously, 6 inches is about the largest size for a standard format screen which can be held comfortably in one hand (perhaps 7 inches for a wide screen device).
A lighter device, such as the Amazon Kindle, can be gripped by the edge with one hand, while operated by the other. However, the classic computer tablet design, where the screen extends to the edge and the device weighs too much to hold by the edge anyway, cannot be operated this way. It has to be propped against the body or placed on a surface.