The Roomba's coverage algorithm looks maddeningly random and inefficient when watched with human eyes, but use a long-exposure camera to track it and you can see how thorough it really is:
Now here's something interesting, I set up a photo camera in my room, turned out all the lights and took a long-exposure shot of my roomba doing it's thing for about 30 minutes. The result is a picture that shows the path of the roomba through it's cleaning cycle, it looks like a flight map or something. It really hits every spot!
(via JWZ's Livejournal)