I'm curious about why in some houses, the Roomba is as effective or more effective than regular vacuums, and in other homes they are less effective than a regular vacuum? What is accounting for that difference?
Is it the brand (i.e., not-actually-a-Roomba-but-a-cheaper-knock-off vs an actual Roomba)?
Is it the type of Actual Roomba (e.g. 300 series vs 750 Pet series)?
The type of mess a household is dealing with (chunks vs crumbs, wet vs dry, etc)?
Size of the home?
Year of model tested?
Mine pulls out more than any regular vacuum has (i.e., when we vacuum first with a regular, and then Roomba goes over it, the carpet is cleaner after Roomba and its bin is full of stuff the first one didn't pick up), does corners and edges, goes over rugs no problem, etc. But I have the fanciest Actual Roomba, (a series of) homes each no bigger than 500 sq feet, low to medium pile carpet, rugs with no fringes, etc. So, perhaps its value depends very much on a variety of factors, including quality of robot, size and type of home, type of mess, etc? Perhaps these are what need to be considered in determining the potential value of a Roomba-style vacuum?
I guess there are some important things to be considered:
1. Floor layout. An open floor plan is much more roomba-friendly than a lot of little rooms.
2. Floor material. I have all tile, so it's great. My search says that roomba does good with carpet too, and heavy rugs. If you have fringes or light throw rugs it can get stuck.
3. Colors. Roomba doesn't understand black floor/rug/decorations on the floor. For some reason it think it is an abyss and can't get through. If you have a black strip on a rug, your roomba may be unable to get past it. If you have black furniture, there is a great chance roomba will bump on it full speed and leave some markings/scratches.
4. Stairs. For obvious reasons, it doesn't do stairs. And if you have some condo/studio/house that is divided on many levels, you have to move it around, and you lose some of the practicality of the "set and forget" schedule.
5. Type of mess. Wet is bad. It will get into the brushes, smudge on the wheels, and instead of a clean home you might end with a lot of marks of the wet mess being dragged around. And it can really damage the device, according to the manual. Dust is fine, crumbs are fine, fur is fine. It pick up hair, but it usually gets tangled in the brushes, so if you have a lot of hair it will be a little harder to clean it. Hardly more than 10 minutes at a time, though.
6. Size. If you have a too big of a home it might get lost and/or without power to come back to the base, or just clean the rooms closest to the base. This problem can be mitigated using the lighthouses of the newer versions. I don't know what is the size threshold for it.
7. Things on the floor. We have cats. Cats love playing with strings. Roomba hates strings. We have to be careful to do not leave strings on the floor, or it gets all tangled and makes roomba stop working and cry for help. My mom has a dog that can't learn to poop on the right place, so she couldn't never have a roomba (unless she likes poop spread all over her house, or if she carefully inspect the house for poop beforehand). Depending on what kind of toys you/your kids/pets leave on the floor, roomba may have a problem with it.
8. Shape of furniture. Depending on the shape of your tables/chairs/things feet, the robot may be able to come up and not come down, and ask for help. If you have mostly square angles things it shouldn't be a problem, but round, curved edges may be troublesome, depending on the angle.
aaaaand, that's the end of my roomba research sheet =P