Bill Gates doesn’t get a lot of credit these days for being a visionary. But when it comes to his relationship with Facebook, he may still be a step ahead of the rest of us. The Sun, a British tabloid, reported this year that Gates had quit his half-hour-a-day Facebook habit, partly because he was getting more than 8,000 “friend” requests daily but also because he was finding “weird fan sites about him.” (View a slideshow of several "weird fan sites.") A Microsoft representative confirms that the boss has gone cold turkey but wouldn’t disclose whether Gates knew of a Facebook group called “Would you have sex with Bill Gates for half of his money?”

Actually, it’s a wonder that Gates was on Facebook in the first place (Microsoft’s $240 million investment in it notwithstanding). Bill Gates obviously doesn’t need to schmooze on Facebook. And neither do you, despite the pressure you’ve doubtless felt to join it (because, y’know, everyone is on Facebook). Perhaps you’re like Ben Rosen, who co-founded venture-capital fund Sevin Rosen, which has bankrolled such companies as Electronic Arts and Compaq (which he once led as C.E.O.). Rosen is hardly averse to sharing personal information online; he says his blog, BenRosen.com, has become a small social network of sorts. But he has yet to use his Facebook account. “I’m trying to figure out the utility for me,” he says.

Or perhaps, like Gates, you just find Facebook a little…creepy. Businesspeople often claim to use Facebook for vague “market research” purposes or to satisfy idle curiosity. But the social norms of social networking are still in flux, making privacy a real issue, says internet-marketing writer David Weinberger. “Younger people violate older people’s idea of proper behavior when it comes to privacy,” he says.

“It’s kind of eerie how much information is available about you on a social network,” says Michael Fertik, C.E.O. of online-privacy service ­Reputation­Defender, “and how many conclusions, tentative or otherwise, can be made so handily, fairly or unfairly, based on that information.” Fertik estimates that all 55 of his employees use Facebook, and although he doesn’t, he’s unsettled by the all-consuming, constant-update M.O. it encourages. “I’ve seen a lot of quiet, passive-aggressive resentments and rumors that come from people just knowing that much about your business,” he says. “If you’re updating people, like, ‘I’m at a barbecue at my colleague’s house,’ someone you work with might ask, ‘Why am I not at that barbecue?’ ’’

The ease with which Facebook can be used to broadcast your whereabouts adds a particularly disturbing dimension for executives who would surround themselves with security in real life but are lulled into complacency by Facebook’s tidy veneer. Last year, the British military sent a directive to its army units to avoid revealing their service connections online—“Be particularly careful if you are on Facebook, MySpace, or Friends Reunited”—fearing that, yes, Al Qaeda could use them to track prey. Your business competitors might not be terrorists per se, but Facebook can be useful for anyone trying to poach your M.V.P.’s.

Even social-networking evangelists are legitimately nervous about Facebook, given its fiasco last fall with Beacon, an advertising engine that automatically announced users’ activities on other sites—revealing their purchases, for example—without the users’ necessarily realizing that their every click was being chronicled. Facebook apologized, but that sort of unwitting dissemination of potentially sensitive information has strengthened the market for Connect­Beam, a consultancy that sets up secure social networks for the corporate intranets of Fortune 500 companies. “­Companies like Honeywell,” says Puneet Gupta, ConnectBeam’s C.E.O., “could not take a chance to put their information on someone else’s cloud”—meaning on the servers of a social-networking site the company doesn’t control.

But Facebook’s ick factor in the executive suite might have as much to do with its shiny, happy world of “friendship” as with security. “There’s almost an inverse relationship between seriousness and how much you participate in social networking,” says ­ReputationDefender’s Fertik, laughing. That basically nails it: Facebook is simply unserious—particularly given how it prompts hard-driving business executives to regress into adolescent vernacular. “Poking” people, requesting “friends,” writing on someone’s “wall”: It’s cute when you’re in high school or college. But in a corporate environment, it sounds disingenuous and downright silly.

Ultimately, Facebook candy-coats the true nature of business relationships. And it will rot your teeth.