The imminent demise of one of the most heavily plugged advertising campaigns on US television has sparked vigorous internet exchanges between Zeta-Jones's fans and industry insiders who questioned the effectiveness of any celebrity in boosting company profits. Her departure will follow a series of advertising fiascos involving prominent Hollywood actresses featured in multi-million-dollar campaigns that were widely deemed to have flopped. Angelina Jolie and Sarah Jessica Parker were in recent clothing promotions that attracted more criticism than customers.

"When you first saw [famous] names in advertisements and on magazine covers it was novel," said one advertising agency executive. "But it's become so ubiquitous it's one big bore." As the perky, glamorous spokeswoman who popped up in every T-Mobile ad, Zeta-Jones became one of Hollywood’s wealthiest actresses. According to Advertising Age magazine, she has earned $20m (£11m) from T-Mobile, Elizabeth Arden and other endorsements.

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Yet the public's seemingly insatiable appetite for celebrity images - fuelled by tabloid magazines and the spread of the internet - encouraged advertisers to dangle huge contracts in front of the Hollywood A-list. Gwyneth Paltrow was signed by Estée Lauder, Nicole Kidman starred in what was billed as the most expensive TV advertisement in history - a two-minute plug for Chanel No 5 perfume costing a reported $43m - and Charlize Theron became a spokeswoman for Christian Dior. The celebrity age appears far from over - L'Oréal has just added Diane Keaton to a line-up that includes Penelope Cruz and Scarlett Johansson - but there is evidence that the tide is turning. Louis Vuitton, the luxury luggage manufacturer, recently returned to professional models after using actresses such as Jennifer Lopez and Uma Thurman. Jolie earned a reported $12m from St John Knits, a US women's clothing brand, but her campaign ran into flak when the company's customers - conservative, wealthy, middle-aged women - rebelled at attempts to reinvent the brand for a younger, trendier market. An expensive campaign for the Gap fashion chain featured Parker, star of Sex and the City, but was found to be "annoying" potential customers, according to market researchers. "Ten years ago, having a celebrity in your ad would class it up," Robert Thompson of Syracuse University told The Wall Street Journal. "Now there’s something cheesy about it . . . there are so many celebrities on so many magazines all the time."

Jonah Bloom, editor of Advertising Age, noted last week that advertisers willing to spend millions of dollars promoting their products rarely did so without careful scrutiny of the performance of their campaigns. "If you see them repeating those ads, they are working," said Bloom. "But do I think that in this day and age a celebrity endorsement is the most effective means of marketing and advertising? Absolutely not. People don't hold these icons in such high regard any more."