(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.