There's a Roomba mailing-list I'm on and someone remarked how his berber carpet wasn't being cleaned as well as he had hoped. Someone on the list replied with a good description of what Roomba excels at, and what it doesn't work so well with. I couldn't find a direct link that wasn't roadblocked, so for a few of you who have contacted me about how well it works can read this.
Roomba's primary function on carpet is as a sweeper. I will not get to dirt that is buried with any depth in the pile. The vacuum relies upon intimate contact with a solid surface and the squeegee flaps and the seal that produces. This 'Seal' cannot be created with rugs, hi-low-or almost no pile. Think of the Roomba as a sweeper on rugs and a sweeper/vacuum on hard floor surfaces.
The Roomba is an extremely competent sweeper however due to the nature of its motor powered high RPM brushes. The vacuum action is pretty effective on hard flooring as per dust and fine debris.
Hopefully in future Roombas they will find a way to produce really powerful vacuum action to work alongside the sweeper action. Producing a powerful vacuum while keeping battery drain to a minimum will be quite an engineering problem.
Some people look at hand vacs like the 'Black and Decker Dust Buster' as ask why can't iRobot make the Roomba as powerful as that?
The Dust Buster and battery powered hand vacs like that are deceptive. First, you will notice that the Dust Buster has a small inlet area. This is not too much different that the concept behind the squeegee flaps on the Roomba. The Dust Buster can get a lot of vacuum action in the small inlet area and it is still effective because this is a spot cleaning tool under human control so you place it in the small areas that need cleaning under the control of human guidance. Even with all that brain power, cleaning a full room with such a small inlet would be a pain by a human.
Secondly, the Dust Buster is designed to only run for approximately 10 minutes so they can suck plenty of current for a short period to run a powerful motor and large impeller. The Roomba could not be effective with a total run time of only 10 minutes. In addition the Roomba power pack must produce energy to power the drive system and brushes too. So getting enough power to produce a powerful vacuum and run the Roomba is a real engineering problem.
I believe that the only way to make a Roomba that is as competent a vacuum as it is a sweeper is to switch to a Lithium Ion power source and consider using rare earth magnet motors.
Lithium packs can probably be made with enough capacity to do the job and still maintain a reasonable size and weight profile. This is of course only a guess based upon my own experience with consumer products and some small knowledge of battery technology.
If iRobot is willing to produce a really rugged Roomba with this technology and capability it will probably be a gamble because the cost will be high and after so may people having negative experiences with the Roomba the early adopters that are traditionally your best way to spread word of mouth may NOT be willing to take a chance again.