With not a penny of paid media and in less than a month, "Dove Evolution," a 75-second viral film created by Ogilvy & Mather, Toronto, for the Unilever brand has reaped more than 1.7 million views on YouTube and has gotten significant play on TV talk shows "Ellen" and "The View" as well as on "Entertainment Tonight." It's also brought the biggest-ever traffic spike to CampaignForRealBeauty.com, three times more than Dove's Super Bowl ad and resulting publicity last year, according to Alexa.com.

By those measures, "Evolution" is the biggest online-buzz generator in the U.S. personal-care and beauty industries, topping this year's effort from Omnicom Group's Tribal DDB on behalf of the Philips Norelco Bodygroom shaver. And that's before the campaign began rolling out to 10 additional countries in Europe, Asia and Latin America last week.

"Dove Evolution" also trounced another October darling of the blogosphere -- would-be investment banker Aleksey Vayner's self-promotional video -- for mentions on Nielsen BuzzMetrics' BlogPulse. And it ranked among the top 15 blog-linked videos last week on Technorati -- the only one, aside from a presentation by Apple's Steven Jobs, from a nonpolitician.

Nobody understands how online viral marketing really works. Worse: ever since big brands discovered its power, it's becoming harder every day to succesfully create some buzz online. It's true that a succesful "word of mouse" campaign is always cheaper to produce than, say, a street ad campaign. And yes, it's a perfect way to support a bigger ad campaign, or reach a different, more "webby" target group. But if a viral campaign is not handled right, it might hit you in the face, and sometimes even harm your brand. Or worse: be ignored completely, like the majority of them. All you can do is: avoid common mistakes, unleash the virus, wait and pray.