You can enter your guess - as a percentage of the amount of multi-colored "dirt" that a Roomba can clean up in an allotted area in two and a half minutes - at the Robots Contest - How good is a Roomba? page on the website Robots, a podcast and forum site for news and views on robots. As a hint, there's even a short (0:31) video of the first few seconds of the Roomba beginning its cleaning:
The contest (which ends September 24th at 9AM GMT) is meant to highlight the field of probabilistic robots, which concerns itself with how intelligent systems can be designed to deal with uncertainty. The authors of the above-mentioned book are associated with the Laboratory of Intelligent Systems in Lausanne, which focuses on the development of robotic systems and artificial intelligence methods inspired by biological principles of self-organization.