A computer with a small footprint can''t have a very large screen, for example. Users may have to resort to using the accessibility features in Windows, such as larger fonts and image magnification, just to do the simplest tasks. Technically, of course, computers can become smaller yet. But machines can get a whole lot smaller than they are now before that becomes a problem. The practical bottleneck is in the human factor.
Eyes can only focus on objects above a certain size.
Fingers can only tap keys accurately if they can strike them individually on cue. Yes, they''re small and light, but the keys on some are so small and close together that you can''t type on them. If they ever went through a usability lab, it was populated by elves. And items that are necessary in today''s computing environment are, oddly enough, optional. The floppy drive, and most of the connectors such as parallel and serial ports, are in additional devices that you have to cart around.