Amazon.com (Nasdaq: AMZN) still isn't coming clean with how many Kindle e-book readers it's selling, but at least now we know that it will be in the "millions" this holiday quarter alone.

In a forum post unearthed by Daring Fireball, an official post in Amazon's Kindle forum claims that the company has already sold millions of the third-generation e-readers since the quarter began. Even if this means that just 2 million Kindles have sold over the past 73 days -- the bare minimum when all we get to chew on is "millions" -- it's still an impressive feat.

The Kindle got off to a bumpy start three years ago, but no one said the e-reader revolution was going to happen overnight. Bibliophile resistance and a stiff $399 price tag kept anyone other than early adopters away.

Sony (NYSE: SNE), Amazon, and a handful of smaller players found it hard to nab mainstream success. Then the leading bookstores got behind the push. Borders (NYSE: BGP) took a stake in Kobo. Barnes & Noble (NYSE: BKS) introduced the Nook. Apple (Nasdaq: AAPL) introduced its iPad tablet, complete with a free copy of Winnie the Pooh to woo the masses.

However, it really wasn't until this year's price war -- driving the price of the Kindle to as low as $139 -- that it all began coming together. Book lovers that figured it would take several dozens of e-book purchases to cover the cost of the $399 model can now justify the lower breakeven point on a $139 reader.

The momentum is clearly building, and that may be bad news for traditional retailers. Borders and Barnes & Noble didn't dive into this model-altering niche to preserve their books-and-mortar empires. They just didn't want to be left behind. They are unlikely to be selling "millions" of their own e-book readers, but let's see if either chain provides a clearer number now that Amazon is raising the bar.

It may be that 2010 proves to be the year when e-book readers became a mainstream gadget. If that's the way history writes it up, there's a better chance than fair that the next generation won't be reading it in a leafy text.

Is this the holiday season for e-book readers? Are you gifting a Kindle or a rival reader this year? Share your thoughts in the comment box below.

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Longtime Fool contributor Rick Munarriz has been shopping online for about as long as Amazon.com has been in business. He does not own shares in any of the stocks in this article. He is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. The Fool has a disclosure policy.