Just before Thanksgiving, the digital video recording company TiVo announced that in March its customers will begin seeing "billboard" advertisements flash across their television screens when they fast-forward through commercials. Many TiVo users were outraged and felt betrayed. Avoiding unwanted advertising is a frequently cited reason for owning a TiVo, and Forrester Research has found that DVR users fast-forward through 92% of commercials. TiVo is a technology of personalization and, like many such technologies (iPod, BlackBerry), its most appealing feature is the degree of control it offers the user.

FCC Chairman Michael Powell once referred to TiVo as "God's machine," but TiVo is less like a deity than a thoughtful butler. It expertly stores and mines an individual viewer's preferences and can make suggestions about shows he or she might like to watch. And although the company has yet to turn a profit, it excels at marketing and presents its product as a savvy technology for the busy individualist. Its slogans -- one of which is "Do More. Miss Nothing" -- invite customers to feel that they are in total control of their television experience. TiVo is all about you.

Or is it? In fact, TiVo was designed to accommodate the needs of the marketplace, especially advertisers, from the beginning; this is the reason you can fast-forward through recorded commercials but not skip them entirely. And the increasing popularity of the DVR -- Forrester Research predicts that in five years, 41% of households in the U.S. will have some form of digital video recorder -- has transformed the way we experience advertising.

DVR users' eagerness to skip commercials has led to more insidious forms of marketing, such as product placement within television shows. Those enormous cups of Coca-Cola on the judges' desk on American Idol were not there by accident. The relationship between TiVo and advertisers is also evident in TiVo's practice of selling information about subscribers to marketers. The company recently signed a deal with Nielsen Media Research to provide detailed (though not individually identifiable) information about customer viewing habits.

But fretting over the intrusions of advertisers misses a broader problem with TiVo: DVR enthusiasts spend more time talking about the technology than on what the technology is encouraging us to do. One of TiVo's slogans is "You've got a life. TiVo gets it, " suggesting that TiVo understands your need for efficient, personalized entertainment. But what TiVo really "gets" about you is that if it's easy and convenient, you're going to spend a lot more of your life watching television.

Reports from Forrester Research and Next Research found that DVR users watch more television after purchasing a DVR -- five to six hours more a week in the latter study. TiVo offers us a more efficient way to perform a task; unfortunately, that task is watching television. Citizens of the industrialized world already spend, on average, three hours a day watching television.

We spend more time watching TV than doing anything else except working and sleeping. And we do this despite sound evidence of television's harmful effects. Researchers at Yale University have found that heavy TV viewing contributes to decreased attention spans and impatience with delay, as well as general feelings of boredom and distraction. Scientific American magazine has reported that television viewers exhibit "passivity and lowered alertness" as well as "less mental stimulation, as measured by alpha brain-wave production, during viewing than during reading."

The journal Pediatrics published research in April showing that "hours of television viewed per day at both ages 1 and 3 was associated with attentional problems at age 7," including attention deficit and hyperactivity disorders. The researchers called for "limiting young children's exposure to television as a medium during formative years of brain development."

Americans have been and will continue to be temperamentally optimistic and libertarian about our technologies, and it is unlikely that we will give up our televisions. But we should not let our enthusiasm for TiVo and other technologies of personalization obscure the negative aspects of a world where everything can be had on demand.

It would be unfortunate if the technologies we embrace for making our lives more efficient ended up freeing us to be merely passive viewers of virtual worlds rather than engaged participants in the real one.

—Christine Rosen is a fellow at the Ethics and Public Policy Center in Washington, and senior editor of The New Atlantis: A Journal of Technology & Society.