Shares of Amazon.com were down almost 10 percent in extended trading after the company posted less-than-stellar earnings for its most recent operating quarter.

Amazon.com generated about $12.95 billion in sales in the fourth quarter of 2010, up 36 percent from $9.5 billion in the same quarter in 2009. The site served as a major hub for shoppers during the holiday season. Holiday sales were quite good by most metrics, so expectations were pretty high for Amazon. The site had 25 percent more unique visitors during the holiday shopping season in 2010 when compared to a year earlier, according to comScore.

But that just wasn’t enough for investors, with its shares dropping to around $166.45. Analysts on Wall Street estimated that the company would bring in $13.01 billion in revenue. While Amazon just barely missed the mark, the fact that it underperformed during what was supposed to be a heavy shopping season — now that the economic recession has for most intents and purposes come to an end — apparently didn’t bode well for the company.

Bezos did his best to spin the news in a positive light, pulling a card from Apple’s deck in exclaiming that the company finally hit a $10 billion quarter (Steve Jobs was on Apple’s third-quarter conference call to commemorate the company’s first $20 billion quarter.) Unfortunately for Bezos, Amazon didn’t have the firepower to crush earnings expectations like Apple typically does. The online retailer’s income was up 8.3 percent, from $384 million in the holiday shopping season in 2009 to $416 million in the fourth quarter of 2010.

The company (as usual) was mum about how many Kindles, the company’s electronic book reader, it sold during the holiday season. The device is typically pegged as one of the top Christmas gifts on many sites. But it did say that for every 100 paperback books sold off Amazon.com, the company sold 115 eBooks for Kindle readers.