Everyone is buzzing about Internet buzz. And it's easy to see why. What marketer could sit by and watch all the hype generated by the JibJab cartoon lampooning the presidential candidates, or the ersatz video missives of Lonelygirl15, without seeing a "Your Business Here" sign plastered onto the images? The buzz believers preach that buzz marketing will trounce traditional advertising, that mastering it is critical to any business, and that its payoffs are as high as its costs are low. The technology consultancy JupiterResearch, which launched a "social marketing" division earlier this year to study and advise on online-buzz-based marketing, reports that about one in five marketers plan to use "online viral marketing tactics" next year--that is, they plan to put something online in the hopes that people will pass it along to everyone they know.

Buzz is new. Buzz is cool. But does online buzz actually work? Good question. Marketing has always been an inexact science at best. But with buzz marketing, it's even harder to find a correlation between Internet mindshare and sales. And that means companies that divert attention and resources from other forms of marketing to pursue online buzz may end up with little in return.

We saw that vividly last summer when the movie Snakes on a Plane, after achieving unprecedented levels of online chatter, failed to deliver opening weekend. Of course, the buzz believers were quick to dismiss the film's dive, trotting out the old adage that nothing kills a bad product faster than good advertising; in other words, the buzz did its job, but the movie sucked. In fact, more than two-thirds of reviewers gave Snakes a thumbs-up, according to Rotten Tomatoes, a website that tracks reviews. ("Honestly satisfying"--The New York Times.)

I'm not suggesting that buzz is somehow bad. It's just that marketers are rushing to achieve it despite the fact that there is no clear evidence that it will pay off in a significant way. "There's an implicit belief that online buzz works," says Patti Williams, an associate professor at the Wharton School who studies Internet marketing. "But the evidence that you can go from online talk about a product to sales is really limited."

You only need to drop in on YouTube a few times a week--or an hour--to see just how perishable fame on the Internet can be.

Of course, none of this proves that online buzz is less effective than other forms of marketing. It's always been challenging to link specific marketing efforts to sales. And offline buzz can disappoint, too. Ever since Alka-Seltzer actually saw sales decline during its beloved "spicy meatball" campaign in 1970, advertisers have known that just because consumers enjoy a marketing message doesn't mean they'll buy the product.

But that fact seems to be particularly true on the Web. Why? For one thing, it's so easy for messages to spread online. Of course, that's precisely what marketers love about online marketing: Blast out a funny video to thousands of bloggers, and word will get out to tens or hundreds of thousands of consumers. Adding to that appeal is that thanks to search engines, it's so simple to measure message spread day by day, and it sure is encouraging to watch those numbers climb. But that lack of friction has a downside. Calling a friend on the phone about a funny commercial or even talking up a new product at the water cooler requires a certain amount of effort. Spending a few seconds to pass on a link to a dozen friends doesn't necessarily mean that anyone really cares.

Making things worse is that the gatekeepers of online buzz--the bloggers--tend to have a sharp, skeptical mindset, more critic than consumer. They may be laughing at you, not with you. Or the online buzzers may simply be different from your target customer. The buzz marketing analysis firm Brandimensions determined that in the summer before its premiere, NBC's Studio 60 was the most buzzed-about show online, turning up in well over twice as many Internet discussions as the new NBC show Heroes; the buzz was more positive than that for Heroes too. But according to its most recent figures, Nielsen, which measures actual viewership, found that Studio 60's audience stood at 7.7 million viewers, compared with Heroes' 13 million viewers. Apparently, online buzzers about television programs don't represent a large cross section of the actual viewing audience. "Online buzz doesn't necessarily translate to the hundreds of millions of people who simply aren't engaged in the blogosphere," says Todd Defren, a principal at public relations agency Shift Communications in Boston. "Blogging is still a small, elite, mostly white event that doesn't always have a lot to do with Joe Average."

What's more, Internet buzz tends to build best over humorous, offbeat, edgy concepts that aren't weighed down by even a hint of overt marketing. That means that there's relatively little opportunity to get any sort of message across, making the link between buzz and sales all the more tenuous. Mentos and Diet Coke got a lot of attention on the Internet recently when people started posting videos of the gaseous fountains created by combining the two products. Coke was not amused. "If there ever was such a thing as marketing message control, there certainly isn't now," says B.L. Ochman, a media consultant who works with Fortune 500 companies to hone Internet marketing strategies.

But perhaps the biggest barrier to converting buzz into sales is the fact that online buzz evaporates fast. Visit JibJab a lot these days? Still talking about Lonelygirl15? You need only drop in on YouTube a few times a week--or an hour, for that matter--to see just how perishable fame on the Internet can be. "What you're doing when you stimulate online attention is throwing out a message that piques interest for a limited time and then quickly fades," says Wharton's Williams.

In fact, contrary to the notion that buzz marketing is a cheap route to exposure for small companies, most of the successful campaigns cited by buzz-centric marketers are big-company projects backed by multimillion-dollar ad budgets. That includes CareerBuilder.com's customizable talking-chimp e-mails and OfficeMax's (hilariously) fake handwriting analysis sessions hawking its Tul pens. Even then, most efforts tend to sink, largely unnoticed. A 2006 survey by e-mail marketing firm Silverpop reports that while viral marketing was all the buzz among e-mail marketers, only one in 10 reported having any success with the approach--and these folks have notoriously low standards for "success."

In spite of the grim prospects for a profitable buzz campaign, Ochman and others insist it's worth trying. And it's hard to argue. Why not throw your video or interactive game or other virtual confection out into the blogosphere and see what happens? The mistake would come with making it a critical factor in your marketing plan. That would be like going into the Super Bowl with a game plan of throwing a Hail Mary.

Besides, some buzz campaigns have delayed, indirect payoffs. I noticed, for example, one way in which Snakes on a Plane is starting to build a market among a very buzz-aware group: It's becoming popular on illegal movie-downloading sites.

Contributing editor David H. Freedman is a Boston-based author of several books about business and technology.