Some, like Mr. Sinclair, have embraced this lifestyle, influenced by a growing sense of just how precarious traditional employment can be and reveling in the other benefits, like flexibility and diversity.

Others, however, would vastly prefer permanent jobs. They have struggled to deal with the instability, the second-tier status often accorded contractors and other temporary workers and the usual lack of benefits. In most states, they are ineligible for unemployment insurance and worker’s compensation. Indeed, it is not at all clear that the shift to these kinds of arrangements is good for workers.

Christine Reams, 45, spent a dozen years as the director of human resources at a large hospital in Columbus, Ohio, but was laid off in July 2008. After struggling for more than a year to find a permanent job, she landed a contract assignment back at her former employer in September, this time in the information services department. Initially, the position, which pays half of what she used to make, was supposed to last only six weeks, but the hospital has extended her contract several times.

Now past her sixth month, she is grateful for the work, but the uncertainty has weighed on her, so much so that she checked herself into the emergency room recently when her blood pressure soared. Without health benefits, she had fretted over whether she would be extended again.

“It’s not permanent,” she said of the assignment. “So I am not feeling secure.”

Bob Longo, 47, of Green Brook, N.J., was laid off as a divisional sales training manager at Unilever in 2006. Since then, he has worked as an independent contractor, stringing together a relatively steady stream of assignments, often several at once.

But he has also had to deal with serious peaks and valleys, and he is now trying to find a permanent job.

Mr. Longo estimates that he has earned slightly more on an annual basis than he did at Unilever. On the other hand, he no longer has health benefits, a company car, a pension or a 401(k). Though he can use his wife’s health insurance, he says he does not have the stomach anymore for the endless cycle of scrabbling for work every time he comes off a project.