Celebrity endorsements used to drive sales of aftershave and washing powder, but the rarefied world of publishing now craves the kind of commercial association it might once have sneered at.
In the British market, being added to Richard and Judy's book club typically increases sales by up to 400 per cent. But Oprah Winfrey's own club in the US, which inspired the Channel 4 equivalent, wields far more clout.
Winfrey's decision to include self-help book A New Earth in her book club, and embark on a global promotional campaign, has turned it into this year's publishing sensation, boosting sales of the Penguin Books title from 500,000 to four million, a far greater uplift than winning the Man Booker prize might generate.
The American book market grew by 2 per cent in 2007, and Winfrey was responsible for half that expansion, according to Penguin's chief executive John Makinson, a former journalist who took over at Penguin in June 2002. The American Association of Book Publishers says the US market was worth $24.2bn in 2006, so Winfrey provided the industry with a $250m fillip last year.
'Oprah and Richard and Judy demonstrate the power of recommendation,' he says. 'With Oprah, it's really her personal taste. Reading a recommendation from her is almost a hypnotic experience. We've now had two "Oprahs" in succession, but this is the first book she's set out to promote globally.'
The chat-show queen hosted a live 'webinar' last week with author Eckhart Tolle and the hype surrounding the title could boost Penguin's profits this year.
Makinson used to edit the Lex column at the Financial Times, which - like Penguin - is part of media giant Pearson, but he stopped writing about businesses to run one, returning to the paper in 1994 as its managing director and rising rapidly through the ranks at Pearson.
Penguin is one of the top three publishers in the UK and the US, and now accounts for 20 per cent of Pearson's turnover and 12 per cent of profits. These days Makinson is even mentioned as a possible successor to Pearson chief executive Marjorie Scardino, but he is quick to rule that out. 'I don't think I am. Nor should I be,' he says.
He is more comfortable talking about the changing dynamics of publishing, which were transformed by the entrance of the big supermarkets in the market at the turn of the decade.
'They decided that selling books at a discount was a good way of driving traffic and they grew and grew for five years, but I think that trend has slowed. Last Christmas was not a big supermarket Christmas compared with 2006.' Independent bookshops are making a comeback, he claims, growing by as much as 14 per cent year-on-year, as customers who want to browse for titles, or seek expert advice, return to smaller outlets.
That may seem surprising at a time when Amazon.com is growing rapidly, but there is little doubt that we are reading more. The total number of books sold in the UK was 237.8 million in 2007, up 5.8 per cent from 224.8 million in 2006, according to market data company Bookscan.
The real challenge to the industry, according to Makinson, comes in a different digital form.
Penguin is one of five publishers (including sister company Pearson Education) taking legal action in the US against Google, which is currently placing tens of thousands of books held in public libraries on its website, making them available to readers free of charge. 'The basis of our legal action is to defend the first principle of copyright, which is based on permission,' Makinson says. 'Google wants to scan the books and give authors the opportunity to opt out.' Publishers want them to ask first, which would slow the project down. In the meantime, the internet giant will continue its land-grab in the hope that by the time the lawyers have resolved the conflict, most of the content will be available to download, and publishers will decide to back down for fear of prompting a consumer backlash.
However, Google is both friend and foe. Penguin supports a separate initiative to place selected chapters or pages from books on its website, which can be a powerful marketing tool.
'I'm happily schizophrenic about our relationship with Google,' Makinson laughs. 'The Google channel undoubtedly stimulates demand for books.'
New technology, in the shape of hand-held devices that enable readers to download digital books, could also transform the way we read, although Makinson points out that 'it's a tiny market, around $1m out of $1.18bn of overall sales'. He doubts the Sony Reader or Amazon's Kindle will have the same impact that the iPod had on the music industry. 'I don't think any of us in publishing see the e-book as an exciting alternative to the book itself for most readers. The book business is different from the music business. Books don't transfer so easily into a digital format, and the music industry was perpetrating the most gigantic con on the consumer by persuading them they wanted to buy an album or CD, when in fact they wanted a compilation.'
The same can't be said of books, he says, despite the fact that anthologies have an enduring appeal.
Penguin's iconic status rests in large part on its design heritage. 'Design has been absolutely central to what we've done,' he says.
Its long list of classics can be repackaged effectively as box sets or series, Makinson points out. The publisher's recent Penguin Ideas series, including short works from Charles Darwin and Friedrich Nietzsche, was a hit. 'If you published the collected works of Sigmund Freud you wouldn't sell many copies. But when you sell Freud in a "great ideas" series you sell lots. We wouldn't be too precious about the brand.'
There are limits, however. Penguin bookshops are unlikely to be popping up on high streets, although its merchandise, including T-shirts, mugs and even a classical CD range, does sell. 'We don't want to push it too hard,' he says.
International expansion provides a potentially more lucrative opportunity. Penguin entered India in the early Eighties, long before most of its competitors, and has 85 per cent of the market for English books. It has recently added titles published in Urdu and other languages, and the Indian market is growing very fast. One long-term aim, Makinson says, is to find the next big-name authors publishing in Hindi or Punjabi and translate them into English, perhaps making it onto Oprah's list once again.
Makinson can't name his own favourite book, perhaps because he reads so many. 'I meet a lot of authors so I do feel some sense of obligation to read what they've written. I don't say to myself "summer's coming, I must revisit [Anthony] Trollope".' If Oprah ever adds the Victorian novelist to her list of favourites, however, you suspect he might rush his collected works on to the market.
The book that won celebrity status
'Counsellor and spiritual teacher' Eckhart Tolle may have written a self-help book, but the German author needed a little assistance from Oprah Winfrey to make it to the top of the New York Times bestseller list. Tolle's work - A New Earth: Awakening to Your Life's Purpose - has now sold four million copies, 80 per cent of which have been purchased since Winfrey made it the latest title in her book club, and threw the full weight of her celebrity status behind it. She is said to keep a copy by her bed.
Her website claims that 500,000 people from around the world logged on to watch Monday's live webcast with Tolle, in which the talk show host and her new favourite author talked about the book's contents.
It is Tolle's fourth book since, as described in A New Earth, 'a profound spiritual transformation virtually dissolved his old identity and radically changed the course of his life.'
The first three; Practising the Power of Now, Stillness Speaks, and The Power of Now, sold well enough, but Winfrey's endorsement has transformed Tolle's latest offering into the publishing sensation of the year. Its 313 pages are, frankly, baffling - a mix of pseudo-science, New Age philosophy and teaching borrowed from established religions - but it has already made him a wealthy man. Educated at London University and Cambridge, according to his website, Tolle claims to have reached spiritual enlightenment at the age of 29 after a life blighted by depression.
Self-help books are big business, and A New Earth is likely to become the biggest one of them all.