Amazon has been famously coy about how many Kindle e-book readers the company has sold. But Mark Mahaney, an analyst at Citigroup, is estimating that Amazon sold 500,000 of the things in 2008, and that the Kindle is on track to become a $1.2 billion business for Amazon by 2010, according to AllThingsD.

The report said that Mahaney came up with his figure by examining a recent filing by Sprint, the company that handles the Kindle's wireless data connection for over-the-air e-book purchases from Amazon. The $1.2 billion figure is a little more suspect, though; essentially he assumed that the Kindle equals the iPod, will do similar business to the iPod at a comparable point in its life cycle, and that customers will buy one e-book per month from Amazon on average.

Meanwhile, everyone—including, presumably, Dick Cheney—is waiting for the other shoe to drop next week, when Amazon has its press conference and unveils Kindle 2.0. Mahaney thinks the new Kindle will be thinner, lighter, have a nicer keyboard arrangement, and cost $299 instead of $359 like the current model. Me, I'm just hoping for page turning technology that doesn't flash the entire screen each time.