According to Advertising Age, as soon as Oprah mentioned the Kindle on her October 24th Oprah's Book Club, Google searches on the term went up fivefold. Traffic directed to Amazon from Oprah.com went through the roof (15,000%) and the aggregate of all visits to Amazon were bumped up 6%, an enormous spike in a mature site. Given these numbers, her Kindle endorsement is a home run for the platform, and should drive huge Christmas sales.
Since Amazon spiffs referring sites 10% of the sale price, Oprah.com stands to rake in over $35 per Kindle sale. And, of course, this establishes the platform as a fulfillment alternative for each subsequent Oprah's book recommendation. Ka-ching!
According to Wikipedia, publishers believe Oprah has 20 to 100 times the sway of any other public figure in driving book sales. For example, a recent announcement that she selected The Story of Edgar Sawtelle by David Wroblewski inspired the publisher to order a run of 750,000 copies. Each one carrying the Oprah selection tag was given its own ISBN to track her impact.