Failure rates can be as high as 20 percent for notebooks in the first year, claims Gartner analyst Leslie Fiering. "The annualized [failure] rate is about 15 percent for desktops by Years 3 and 4 but is about 28 percent for notebooks in Year 3 and can be as much as 35 percent in Year 4."

Those statistics don't stop businesses from trying to squeeze the maximum life from their laptops, however. "We hang on to them until they die, typically," says Mark Flieger, vice president of information services at Occupational Health & Rehabilitation Inc. in Hingham, Mass. But, he acknowledges, "when you start getting beyond four to five years, they start dropping like flies."

"We start to see problems develop in the fourth year," says Michael Kahn, vice president of technology planning at The Bank of New York Co. While hard drives and power supplies are the most likely desktop PC components to fail, with laptops, the screens tend to crack. "That seems to be our biggest problem," he says.

Paul Melnyk, director of the business technology group at Alias Systems Inc. in Toronto, says a four-to-five-year cycle for laptops is about right. "We have units that are 5 years old and going strong," he says. To make them last, he rotates in newer units and puts the older ones in a loaner pool for employees who have desktops and need systems for occasional travel.

Keyboards, power supplies and CPU cooling fans are other common failure points, especially on desktops, users and vendors say. "With our servers, it's just mostly power supplies and fans," says Dunham.