The biggest celebrity backer of Amazon.com's (Nasdaq: AMZN) Kindle may have a new book beau.

Oprah Winfrey was gushing over Apple's (Nasdaq: AAPL) iPad during her show last Wednesday.

"It's going to change the way kids learn," she told her audience, as retold by WSJ.com's Digits blog. She has owned an iPad since the gadget's launch earlier this month.

Winfrey's admiration may not be all that different than the typical Apple fan, but she also has a little history with the device that stands the most to lose if the iPad takes off. After having Amazon CEO Jeff Bezos on her show two years ago, she became the Kindle's loudest cheerleader.

"It's absolutely my new favorite favorite thing in the world," she said on her Kindle-centric show, even giving viewers a promotional code for a $50 price break. This was back in October 2008 -- just months before a new model would render Winfrey's discounted ones passe.

Again, there's nothing wrong with a tech-savvy celebrity professing love for rival platforms. However, there's one interesting quote from last week's show.

"There's a Kindle app so that those of you have Kindles -- obviously I had a Kindle -- you can take all the books from your Kindle and put them on your iPad."

She had a Kindle? She's promoting the ability to migrate Kindle e-books to the new platform? She also discussed the backlit screen and the ability to share photos and play games -- clearly going where no Kindle has gone before.

Suddenly, a stand-alone e-book reader feels like a Swiss Army Knife with only a toenail clipper in its arsenal. This is clearly bad news for the Kindle, Sony's (NYSE: SNE) Reader, and Barnes & Noble's (NYSE: BKS) Nook. They may be cheaper than even the entry-level $499 iPad, but it's hard to be a one-trick pony competing against Apple's loaded stable.

Amazon doesn't have to be a loser if the iPad reigns supreme. Portable connectivity on the 3G iPad models that hit consumers on Friday will help Amazon's e-commerce initiatives. These things are going to be real money savers at the mall when a little comparison shopping is in order. With e-book prices seemingly heading higher as Apple and Amazon embrace the agency pricing model, Amazon may also come out a winner if its Kindle bookstore app proves popular on the iPad.

However, whatever Bezos did to get Winfrey to sing his company's praises two years ago needs to be repeated. He can't let the influential celebrity go too far down Apple's path.

How influential is Oprah Winfrey when it comes to e-books and tech gadgetry? Share your thoughts in the comment box below

Apple and Amazon.com are Motley Fool Stock Advisor recommendations. Try any of our Foolish newsletter services, free for 30 days.  

Longtime Fool contributor Rick Munarriz has been a Kindle owner since 2008 and will be an iPad owner come Friday. He is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. He does not own shares in any of the companies in this story. The Fool has a disclosure policy.