(FORTUNE Magazine) – Looking for a job online? Sending your resume all over creation and getting nowhere? Sure, the job market is still wobbly, but it's also possible that you're inadvertently tripping over your own feet. "When it comes to using the Internet to find a job, a lot of very smart people are making some very stupid mistakes," says Marc Cenedella, a former senior vice president at HotJobs.com who's now president of TheLadders.com, a newsletter and job board for $100,000-a-year-plus executives. Having looked at thousands of resumes, he finds it "kind of amazing how many blunders are committed by some of the most talented people in the world." Why is that? "Most senior managers are just not skilled job seekers. It's something they haven't had to do very often in their lives, so they've never gotten good at it," Cenedella says. "Then you add a high level of stress and anxiety to the equation, and it seems that people often just aren't thinking very clearly."

What are those folks doing wrong exactly? Many, it seems, are putting together resumes that say, in essence, "Hey! I can do anything!" A jack-of-all-trades resume, listing two pages of diverse experience with no particular focus, is "the biggest mistake people make without realizing that it is a mistake," Cenedella says. "Sure, versatility, flexibility, and a wide range of experience are all great things, but an employer wants to fill a particular job. If an orchestra is looking for a flute player, telling them how much you love all kinds of music is not going to get you an interview." The nature of the Internet itself is partly to blame for this problem, since it's turned job hunting into "a direct-marketing game," says Cenedella. "Hiring managers are getting thousands of resumes a day for each opening," and you may need to send hundreds of resumes to get a response from even a few employers. And the more targeted those resumes are, the better. So how do you customize that many? "Obviously you can't," says Cenedella, "but you can do it by categories. A sales resume is different from a sales-management resume, which is different from a marketing resume." Sending the wrong one will land you in limbo.

What else can trip you up? One widespread goof is mismerged cover letters. Since the body of an e-mail is the online version of a traditional cover letter, it's easy to cut and paste copies of the same letter to different companies. Unfortunately, it's also easy to hit "send" on an e-mail that says, "I'd like to put my skills to work at IBM" when you're actually applying for a job at Hewlett-Packard. You'd be smart, too, to forget fancy fonts and colors. "In the body of an e-mail, use plain text," Cenedella says. "It's the only way to ensure that your letter won't turn into gibberish on an outside e-mail system." And then--here's the big thing--turn off your computer. "Hitting 'send' is not the end," says Cenedella. "You still need to get on the phone, take people to lunch, and work your way to the top of the resume pile the old-fashioned way." Plus ca change...