Kip and I got a Roomba (the robot vacuum cleaner) for Christmas. It's roughly circular, about the size of a serving plate (bigger than a dinner plate), and about three inches tall. When you turn it on, it plays a triumphant little phrase, starts up, and works its way out in a spiral for three or four circles, then takes off in a straight line until it hits the wall. Everytime it hits something it turns (sometimes sharply, sometimes slightly) and takes off in a different direction (sometimes straight, sometimes in a spiral). It seems to have some way of telling whether the room is small or big (mean free path, maybe?), as it takes noticeably less time to decide it's finished with a small room. When it thinks it's done, it stops, plays another triumphant little phrase, and waits to be picked up. If you don't pick it up after a few minutes, it turns itself off. It's not very efficient, but it eventually covers the whole floor, and it does a fine job on wood and linoleum, and an okay job on carpet. You still have to pick up the floor first--the Roomba's got no judgement and no way to move electrical cords and such out of the way. But then you set it down, shut the doors and go about your business while it cleans the floor.

So far the floors are noticeably cleaner. :-)