While it could possibly have something to say on the matter at its big event next week, Amazon has so far been mum on the total number of Kindles sold, which has prompted folks like Citigroup analyst Mark Mahaney to do their own digging / speculating to arrive at some hard numbers. Apparently, Mahaney was able to determine that Amazon sold about 500,000 Kindles in 2008 by examining the company's agreement with Sprint, which seems to be a reasonable enough conclusion, although things get decidedly more speculative from there. According to Mahaney, the Kindle will be a $1.2 billion business for Amazon by 2010, assuming that the rate of adoption is similar to that of the iPod at the time of its introduction, and assuming that each Kindle user buys at least one book a month -- two pretty big assumptions, to say the least. As you might have guessed, Mahaney also has a bit to say about the seemingly imminent Kindle 2.0, which he speculates will be thinner and longer than the current model, won't boast a color screen or a touch screen, and possibly cost as low as $300. As they say, stay tuned.