"Several research reports, both recently published and not yet published, provide evidence of the limits of multitasking. The findings, according to neuroscientists, psychologists and management professors, suggest that many people would be wise to curb their multitasking behavior when working in an office, studying or driving a car.

These experts have some basic advice. Check e-mail messages once an hour, at most. Listening to soothing background music while studying may improve concentration. But other distractions - most songs with lyrics, instant messaging, television shows - hamper performance. Driving while talking on a cellphone, even with a hands-free headset, is a bad idea.

In short, the answer appears to lie in managing the technology, instead of merely yielding to its incessant tug.

...The human brain, with its hundred billion neurons and hundreds of trillions of synaptic connections, is a cognitive powerhouse in many ways. 'But a core limitation is an inability to concentrate on two things at once,' said René Marois, a neuroscientist and director of the Human Information Processing Laboratory at Vanderbilt University.

Mr. Marois and three other Vanderbilt researchers reported in an article last December in the journal Neuron that they used magnetic resonance imaging to pinpoint the bottleneck in the brain and to measure how much efficiency is lost when trying to handle two tasks at once.

Study participants were given two tasks and were asked to respond to sounds and images. The first was to press the correct key on a computer keyboard after hearing one of eight sounds. The other task was to speak the correct vowel after seeing one of eight images.

The researchers said that they did not see a delay if the participants were given the tasks one at a time. But the researchers found that response to the second task was delayed by up to a second when the study participants were given the two tasks at about the same time.

In many daily tasks, of course, a lost second is unimportant. But one implication of the Vanderbilt research, Mr. Marois said, is that talking on a cellphone while driving a car is dangerous. A one-second delay in response time at 60 miles an hour could be fatal, he noted.

...The productivity lost by overtaxed multitaskers cannot be measured precisely, but it is probably a lot. Jonathan B. Spira, chief analyst at Basex, a business-research firm, estimates the cost of interruptions to the American economy at nearly $650 billion a year.

That total is an update of research published 18 months ago, based on surveys and interviews with professionals and office workers, which concluded that 28 percent of their time was spent on what they deemed interruptions and recovery time before they returned to their main tasks."

"Recently I've found myself annoyed by how busy my friends seem. Putting aside the possibility that they are avoiding me, some are so on the go that they barely have time to tell me they do not have time to talk. Every phone call, no matter how short, seems to be interrupted by several others. That is, of course, if I actually get a live person on the other end of the phone.

I consider my life to be somewhat filled and fulfilling. I have a husband and two children, work part time, volunteer, exercise several times a week (well, usually) and socialize regularly. For the record, I do not have a baby sitter, but do have a house cleaner for about four hours every two weeks.

But, and I am almost embarrassed to admit this, I also have time to read novels, catch a movie or play once in a while and have the occasional long lunch with a friend.

In our busy, busy world, however, I sometimes feel as if I am the odd one out. Although those who are overworked and overwhelmed complain ceaselessly, it is often with an undertone of boastfulness; the hidden message is that I'm so busy because I'm so important.

...Not only are we constantly occupied, but we, as Americans, are also famous for not knowing how to be unoccupied.

My husband and I would no more fail to use up vacation time than we would hand back our paycheck. But, according to a 2005 study, "Overwork in America," released by the nonprofit group Families and Work Institute, 36 percent of 1,000 salaried employees surveyed by telephone said they did not plan to take their full vacation.

Of course, it is not just in the work force that people are madly busy. Many people I know, who might be able to enjoy some downtime because their children are in school and they do not have paying jobs, pile errands on top of volunteering on top of working out on top of, well, you name it. When the children get out of school, they race from one activity to another, and if at some point life seems to calm down, then it is time to take on a big construction project, get a dog or have another baby."

Social science research documents a number of negative effects of full-time maternal employment on the well-being of children, but what about the impact on the well-being of mothers? While policymakers around the globe continue to push for more mothers to work full-time outside the home, a new study by researchers at the University of Queensland finds that combining motherhood and full-time employment yields a significant "health burden" for women.

Looking at the responses of more than 2,200 Australian men and women who responded to the "Negotiating the Lifecourse" study, a longitudinal panel study conducted in two waves (1996-97 and 2000), the researchers studied the interaction of employment and parental status on self-reported health. While their most complex statistical model found no significant interactions between these variables for men, it yielded key correlations for women, suggesting that "work and family commitments operate differently for men than women." For example, having children under 18 significantly lowered the odds of reporting poor health for women not working outside the home (p<.05) or only working part-time (p<.01), compared to their peers working full-time outside the home. In other words, for mothers with children, working outside the home full-time represents a health risk whereas staying at home (or only working part-time) represents a health benefit.

As their findings found greater similarities between mothers who work part-time with women who did not work at all, the researchers suggest that studies that do not differentiate between full- and part-time employment overlook important differences among women.

The analysis also yielded statistically significant correlations between marriage and health among women, but not men. In the most complex interaction model, previously married women (separated, divorced, or widowed) as well as cohabiting women were more likely to report poorer health than married women (p<.05 for both variables). Women who never married were also more likely to report poor health, but the association was not statistically significant.