RE: The Roomba is not a vacuum cleaner!
Actually, the roomba is part vacuum cleaner, complete with suction and filter, although it's pretty limited. It works basically this way;
as it travels forward, the first thing that contacts the floor is a big rotating agitator brush. It kicks the larger stuff, hair, etc. up towards the back of the roomba, where a second smaller rotating rubber brush flips it backwards into the waste container. Directly behind the brushes are 2 closely spaced stationary rubber wipers that just touch the floor. above the narrow space between the wipers is a waste area and filter and above that is a suction fan, which blows out a vent in the back. As the wipers drag across the floor the smaller stuff, dust, and small hair is sucked up between the wipers and caught by the filter. To empty it you pull off the whole back of the roomba, dump out the big stuff, and slide out the filter assembly, which dumps out all the dust and small stuff.
It is a lot like the manual sweeper thingy that the above poster described, but with the addition of a slightly-less-powerful-than-a-Dust-buster vacuum.
It's great for hard floors, and can handle real low carpets and rugs. real low. It gets over threshholds and minor obstacles no problem. It gets a hardwood floor as clean as you can get it with a broom, maybe better, but it can't get into deep corners or under shallow furniture and it won't pick up the dog toys for you before it vacuums. It does ok on low carpet and rugs, better than you would sweeping them with a broom, but not like a real vacuum. Loose things like string and pieces of clothing, and those little subscription cards that come cascading out of any new magazine, will all get jammed up in the brush and cause roomba to give up and pout.
It's a weird combination of really cool, and completely dorky. It will actually vacuum, your whole house and then drive back to its charging station and park, which is cool. But it gets around basically by driving until it runs head first into something and then it backs up turns and tries again - dorky. It has some cool behaviors where it will work its way around obstacles by turning in a circle around the obstacle till it hits it then slightly adjusting the curve of the circle wider and trying again. That way it can clean around table legs and work the edges of the floor, following the contour of the wall. Then it has this thing where if it gets onto a carpet or some other surface that it can't move forward against and it gets kind of stuck, it will do this crazy reverse bootie dance thing where it backs up just a little bit real fast, which causes its butt to stick up in the air, stops quick, then does it again. It's freaking hilarious. It looks like an epileptic cat in heat. Usually this just ends with it stuck, ass in the air, up against a wall or something. It does have these IR 'virtual wall' things that you can use to fence off areas that you don't want it going into.
Roomba is pretty loud, it sounds like a chainsaw made of plastic, so you want to start it right before you leave for work or the store. And don't make the mistake of watching it or you will just end up following it around, muttering at it about how it already cleaned that part, and picking it up to 'help' it. They clean the floor almost randomly so they aren't efficient in the sense that they do clean the whole floor but in the process the go over some spots many times.
I've had one for about a year and a half, and for my situation it's the shiznit! I live in a 600 sq' hw floor house with 2 dogs and a girlfriend with allergies. Before roomba i vacuumed the floor every day or 2 at the most. Now i vacuum the area rugs and the corners and edges once a week. And roomba gets under the bed and under the computer desk and a few other spots like that that i usually neglected. I dump out better than a double handful of hair, dust, crumbs and worse every day. It really is amazing how much crap it picks up. You do have to walk around and pick up toys, shoes, magazines etc. or it will just vacuum around your shoe, tear up the magazine, and half-eat one of the toys and get all jammed up. I just walk around the house once to pick up and then hit go before I walk out the door to work.
It's not going to work for everyone, if you have mostly carpet or lots of delicate furniture that you don't want it ramming into everyday, it's not for you. But it does do a great job of keeping hard floors clean with a ton less work than sweeping every day. It guess it saves me around 40 minutes a week, and keeps the floor cleaner than i would. On the other hand it takes about 40 min a day to do its thing so it's really taking 5-7 times as long to clean the floors, but it gets them a little cleaner than the alternative (me), and it saves a little of my time. The major pay off for us is the reduction in allergens from getting all that dust and crap out of the house daily, instead of letting it build up for a week. It makes a very significant difference.
As you may be able to tell, i really like my roomba, my girlfriend thinks maybe a little too much. :-)