Now that you've landed a new job, you can't wait to tell your old boss to shove it. Better reconsider. These days it's more critical than ever to make a graceful exit.

SUE BIRCH THOUGHT she had a live one. Last year, the human-resources specialist for database marketer Acxiom (ACXM) recruited a woman for a temp-to-hire administrative job in the Chicago office. "She said in the interview that she wanted to learn to skydive," says Burch. "I thought we'd found a risk taker."

Her first day, the new hire was introduced to everyone in the office and taken to a meeting. Later her supervisors were showing her the email and phone systems when she excused herself to go to the bathroom. She never came back. "We were panicked," Burch says. "We were afraid she'd fallen down, or gone to the parking lot and gotten mugged." But no, the woman had simply walked off the job, overwhelmed by her new duties.

On bad days we all might fantasize about marching out of the office and never coming back, but the reality is, quitting is usually a much more complicated affair. And as people job-hop more and more, knowing how to throw in the towel has become an essential skill. "It used to be that quitting meant saying goodbye. Now you're saying au revoir -- to meet again," says Barbara Moses, author of "The Good News About Careers." Even if you never return to that company, odds are you'll work with some former colleagues again.

The first quandary in quitting is how much notice to give. "I don't know where two weeks came from," says Jeff Moore, president of the human-resources consulting firm Prairie Pacific. "For any type of professional position, you won't be replaced in that amount of time." Assuming your new boss is willing to wait, Moore suggests letting your old employer decide how long you stay on.

Nneka Achufusi is glad she gave a full month's notice before leaving as a senior auditor at a Bethesda, Md., accounting firm. The early heads-up -- and that she waited until after tax season -- allowed her to stay on good terms with her former boss. That was fortunate for Achufusi, since it turned out she didn't like the stuffy atmosphere at the smaller firm she joined. Within four months she was back at her old job. "The fact that I hadn't left them in a bind definitely made it easier," she says.

An even more delicate issue is how to give notice. If you're leaving because you don't get along with your supervisor, there's bound to be animosity, so keep the meeting brief. Let your boss know you'll do whatever is needed to tie up loose ends and cite something positive about your experience there. If you have issues with your boss, don't unload them on him. "The person you will want for a reference -- someone you trust -- is the person you should be sharing constructive criticism with," Moore says.

Just don't put it in writing, cautions Roger Sommer, vice president of the human resources firm Spherion. A resignation letter is not even necessary anymore except at the most traditional firms and at the highest levels. But if you do write one, remember that it has permanence. "I wouldn't put anything negative in," says Sommer. A sour-grapes letter could keep you off the short list if you ever try to return.

Burning bridges was hardly a concern to Kevin Troxall when he left his job as a paralegal at a large New York law firm two years ago. He was moving to Chicago for a job as a television-production assistant, and just before he left he sent an email to the entire company. To call it inflammatory is to put it mildly: "I basically told these people to get a life," he says. "They spent so much time there, they never saw their families. And then I also wrote, 'There are a select few (attorneys) who have been a**holes' and gave their initials. Then I hit the send button and walked out the door."

Though the act was liberating at the time, Troxall began to regret it when the television job fell through two months later. When he started looking for work, a headhunter asked for the name of someone at his old law firm to use as a reference. Troxall tried to hit up an attorney he had been close with, but "he didn't think it was such a good idea." Troxall ultimately did find a paralegal job in Chicago but acknowledges he'd have a tough time ever coming back to a New York firm.

A vitriolic email isn't the only thing you should avoid leaving behind. Burch knows of employees who have forgotten to delete embarrassing bookmarks from their Web browsers. Another potential blunder: leaving your résumé on your office PC, particularly if you've embellished your job responsibilities. So what should you leave behind? An easy-to-follow paper trail so your replacement can pick up where you left off.

While it's a good gesture to make yourself available for questions after you depart, don't be shy to cut the cord. Sommer's advice: After a few calls from your old employer, "tell them you'd be happy to help -- and give them your hourly rate."