In the near future, there may be computers which are roughly the size and shape of pens, albeit a bit thicker -- and that will include the CPU, the monitor, and the keyboard. At least, that's what Bill Gates claimed recently.
The "pens" will be mounted on a tripod; one projecting the images we're used to seeing in our monitors on a wall, while the other projects a kind of virtual keyboard on a tabletop.
I This neat laser based system will allow you to have a full keyboard with your cell phone or PDA and yet only have the inconvenience of carrying an extra pen around. With laptops getting more powerful and smaller by the day, it's possible we may see these devices before long.