LOVING IT: KFC recently offered a free-meal promotion on talk-show host Oprah Winfrey's website ... but feathers really started to fly when the link to the voucher hit Twitter.

KFC, the fast-food chain, learnt a thing or two about the power of Twitter, the messaging site that allows members to post 140-character updates for all to see, when it launched grilled chicken earlier this year.

Something of a departure for the fried-chicken specialist, the company's move into grilled chicken was unveiled by Oprah Winfrey on her show, with details of a voucher on her website for a free meal.

Once the link to the voucher hit Twitter, it was quickly forwarded to millions of users.

"The Kentucky Grilled Chicken launch made a particularly big splash in the Twitterverse," says KFC. "During the online discussion of our free meal, KFC became the top trending topic on Twitter, which is an amazing accomplishment for a brand."

KFC and DraftFCB, its advertising agency, were anticipating a rush after the promotion but demand was so high that the voucher's web page crashed and its restaurants were overwhelmed. Still, in the world of viral marketing, where generating a buzz is all important, the campaign was a huge hit that led to a huge amount of free press coverage even though some of that was critical of KFC's ability to manage demand.

If last year's must-have accessory for the clued-in marketing manager was a Facebook page, this year Twitter is the place for brands to see and be seen. While it remains some way behind Facebook in total members, Twitter has recorded stratospheric growth since the start of the year. It has more than 32-million monthly unique users, according to comScore, an agency that measures web traffic.

But as advertisers have flocked to the site, there have been casualties along the way. The same power to amplify promotions and positive messages also means that any missteps on Twitter are very public ones.

As KFC showed, brands have been quick to see the importance of Twitter's "trending topics", a list of popular phrases that appear on a user's Twitter homepage. Clicking on a trend takes the user to a list of the latest "tweets" featuring that word or phrase. This can be a useful tool for marketers but it also requires careful management.

Habitat, the high-street furniture retailer, found itself the subject of a witch hunt on Twitter after it used phrases relating to the contested Iranian elections to boost its mailing list. "#MOUSAVI Join the database for free to win a £1000 gift card", read one tweet, referring to the opposition candidate in Iran's recent presidential elections, whose supporters have used Twitter to organise a series of demonstrations and to communicate.

Habitat has since deleted the offending messages, which it claims were posted by an unnamed intern, and apologised. "We have been listening to the feedback on Twitter and we are learning more and more about how the community would like us to engage with them," the company.

Even though it said social media sites were a "huge opportunity to hear people's views", Habitat has not returned to Twitter since late last month and would not say when it intended to start posting messages again. Some Twitterers, including a former BBC manager with thousands of followers, have kept the story alive by trying to find the intern Habitat blamed.

"The Habitat story went everywhere very quickly," says Daljit Bhurji, MD of Diffusion PR. "They realised the hard way if you give Twitter posting duties to someone with no experience of how social media works, it will come back and bite you. It's made a lot of clients more nervous."

Bhurji recommends listening to what is said on Twitter before joining, to inform your tone and the issues to tweet about.

"Think before you tweet" is one of his maxims.

The most popular Twitter accounts are those that do more than just post lists of links to brands' websites or vouchers. According to Will McInnes, co-founder of NixonMcInnes, the social media agency, many marketers on Twitter have forgotten that engaging consumers on the internet requires more subtlety than simply broadcasting their messages.

"What people like is help and utility and value," he says. "Most of our clients have substantial multimillion-pound investments in customer service and those are the people we need to get online."

Indeed, many successful corporate Twitter accounts are more an extension of a customer call centre than part of the marketing department.

Whole Foods, the US organic grocer, has accrued more than 1-million followers on Twitter since joining a year ago, not least because of quick responses to what it says is a "very knowledgeable" customer base.

"Certainly at times we've encouraged folks to follow us with contests and promotions exclusive to Twitter," says Winnie Hsia, Whole Foods' social media specialist. But mostly it is "customer service, and valuable and relevant content that keeps folks following us".

Whole Foods aims to respond to questions within 24 hours, and many are answered much faster.

It tends to limit its replies to direct questions.

"We find that only responding to folks who seek us out or formally mention us is less invasive than listening to and responding to all instances of our name being mentioned," she says.

Ben Ayres, one of two permanent ITV employees who run the broadcaster's 10 Twitter accounts, says brands "have to have a personality". Marketers should not be too sensitive about speaking in public, he says. "There is a skill in that - it comes from knowing the brand, but not taking it all too seriously."

ITV's Twitter profiles, which promote shows such as Coronation Street and This Morning as well as its Tour de France and football coverage, have thousands of followers and generate a "significant amount of referrals for us", says Ayres.

Those are most obvious during live shows such as Britain's Got Talent, which dominated Twitter's trends when it was broadcast as fans chatted about the contest.

Ayres recommends timing tweets to coincide with periods of high online activity, such as mornings, lunchtimes and the workday "late afternoon lull".

Advocates admit that it can be hard for companies to measure Twitter's value for anything more than referrals to websites.

One exchange on Twitter suggests its achievements could go further. Coca-Cola and Pepsi are virtual friends on Twitter, at the prompting of digital agency Amnesia Razorfish.

Responding to a "gracious (but competitive) hello" from Coca-Cola, Pepsi replied: "Can rivals and tweeps coexist? We're willing to find out. :)" ©Financial Times