Roombas by iRobot are scooting around 1.2 million homes, but none of my friends owns one -- or their Rolls-Royce-priced counterparts, the Trilobite by Electrolux or Karcher's RoboCleaner. I encounter people every day, though, whose desire for such a robotic vacuum cleaner is right up there with wanting a flat-screen television, sports car or an all-expenses-paid trip to the Riviera.

Lately, usually as I'm loading the dishwasher, for some reason, I've been pondering the concepts of baglessness, centrifugal force, microfiltration, allergens -- stop me if you've heard all this -- dust mites, Hoover's WindTunnel technology and cyclonics, even though I don't need more suctioning devices. I own several uprights, as well as a devilish little one I wrongly imagined I'd use every day to keep ahead of cat hair, and a wet-dry vac for unspeakable disasters.

I have vacuum cleaner on the brain. It is reassuring to know that, in this at least, I am not odd.

The other day I saw a family carting a $500 upright purple Dyson DC07 Animal. (Unlike the Roomba, it needs a human to get anything done.) The wife was quivering with excitement and profusely thanking her husband for buying the cleaning device. He had that manly stride -- the type used by hunters when they bag a deer -- and was babbling about "HEPA" and "high-suck."

Another woman told me her Roomba got more cooing attention at a recent dinner party than either her puppy or toddler. A woman behind me on an escalator in White Flint Mall the other day had just purchased her second Roomba (the upgraded Discovery model for $280) from the Sharper Image and was beaming. "I love it," she said, even taking the blame for the death of her first one because "I used it too much."

Why are vacuum cleaners on our radar screens? And why now? Why has any millimeter of our attention been given over to thoughts of a household appliance that once was a symbol of oppressed housewives but currently, in some quarters, is an object of envy? For my money, we should be obsessing about a machine that loads the dishwasher without human help.

There are many obvious reasons vacuum cleaners have sucked us into their vortex like so many cookie crumbs.

Most of them have to do with good old American marketing skills -- there's lots of competition, lots of ads, the desire to keep up with the Joneses, the argument that the bigger houses of today could use a second vacuum so one doesn't have to be lugged up and down the steps. And so on.

And it's impossible to discount the phenomenon of "trading up" described by Michael J. Silverstein and Neil Fiske in their book of the same name: spending more money on something to treat ourselves -- even if we don't need it.

There are two other explanations. Both theories cast consumers as victims of fate and progress.

The first is the swinging pendulum theory. It has to do with the past repeating itself.

Vacuum cleaners of some sort date to the mid-1800s, says Ann Haines, operations coordinator of the Hoover Historical Center at Walsh University in North Canton, Ohio. The first electric one was developed in 1905, but it weighed about 100 pounds.

In 1907, Ohio janitor James Murray Spangler used a pillowcase, broomstick and a fan to create the first really usable electric one. He showed it to his cousin, Susan Hoover, who was married to you-know-who. William Hoover bought into the Spangler idea and things took off.

The important part is this: Note that the last big push on vacuum cleaners occurred during the Industrial Revolution, when people were hellbent on making housework easier with convenience products. This occurred around the turn of the century before the last turn of the century.

What's more, according to Charles Lester, a vacuum-cleaner collector and proprietor of the Vintage Vacuum Cleaner Museum Web site, scary advertising about household germs and filth at the time the first Hoovers were being produced egged on enthusiasm for the invention.

Sound familiar? Germ-phobic? Craving convenience? Lots of scary advertising?

Then, as now, disinfectants, household cleaners and expensive cleaning apparatus were sought after.

The second explanation is advocated by Neena Buck, vice president of Emerging Frontiers Practice, a division of the market research firm Strategy Analytics of Newton, Mass. Buck specializes in robotics. She credits our preoccupation with vacuum cleaners to the Roomba.

"No one predicted, or could have predicted, that the first successful consumer robotic appliance would be a vacuum cleaner. I mean, the vacuum cleaner industry was staid for so many years. It changed only incrementally. And then a company such as iRobot comes along and thinks about vacuum cleaners in a whole different way," she says.

It put the vacuum cleaner industry into high gear. Every company wants to create a "me-too" version. She says she was at a recent robotics conference in California and looked around at the attendees. "I saw more vacuum cleaning company representatives" -- who had never been present before -- "than anyone else."

Buck thinks the emergence of a vacuum cleaner as the first really viable home robot is logical. She says navigation and avoidance are among the many tasks robots have to perform. Compared with, say, manipulation, which would be required for dishwasher-loading, navigation/avoidance is much easier.

Positively giddy about her own Roomba, Buck also notes that the excitement over vacuum cleaners signifies a new generation of thought that goes beyond wanting a clean house.

In the 1970s and '80s, we were tethered to our devices in our homes (televisions, computers, etc.). In the 1990s, we expected our devices to be untethered (remotes, cell phones, personal digital assistants), Buck says.

We've now entered a time frame in which we will expect things to move around when we require them to, things that will do things for us, Buck says.

Like load the dishwasher? Millions of us live for the day.

IRobot's Roomba (no human propulsion required) has piqued interest in vacuum cleaners.