The next big wave of changes in computers has already begun, with solid-state data storage. Compared to magnetic and optical drives, they're not only smaller and lighter, but also less energy-demanding. Open up the case of a standard desktop computer and look at what takes up most of the space: drives, a power supply unit, and cables to and from those parts.
The remainder is mostly the motherboard, CPU, CPU cooler, and RAM, but various handheld gizmos have been using smaller, simpler versions of those (minus the cooler, which isn't needed when things are that tiny) have already been in use for quite a while, as long as the programming is simple enough to be done on this more limited hardware. So magnetic and optical disk drives, and the power supply units to feed them, were the only things left that justified a desktop computer's bulk. Replace them with flash memory, and accept not getting the very fastest performance that can possibly be achieved this month, and you have no reason for the computer (minus keyboard & monitor, at least) to be significantly larger than a PDA or
OQO. So the big separate "tower" part of computers will be no longer made and gradually disappearing as the old ones get replaced with tiny computers like the OQO, bought not just for portability but also because even if all you do is park it at home as the home computer, you can put them practically anywhere and hide them in unobstrusive little corners, instead of having to arrange rooms around them and buy special furniture for them. The most space-consuming parts will then be the keyboard and monitor (which might themselves be good things behind which to "hide" the computer).