Don't hold your breath for Amazon.com to release sales data for its Kindle electronic reader. CEO Jeff Bezos, speaking at the company's annual shareholder meeting in Seattle today, said Amazon may never reveal Kindle numbers -- and their impact on Amazon's bottom line. Bezos, speaking to shareholders at the Seattle Art Museum, also touched on the economy, cloud computing, and a certain cheesy black T-shirt.

Bezos told the crowd that Kindle is gaining traction, noting that for books with a Kindle digital version, Kindle sales represent 35 percent of those books' overall sales. He said Amazon has been aggressively adding Kindle content, with the number of Kindle books growing from 90,000 titles 18 months ago to over 285,000 today.

But Bezos was tight-lipped when asked for actual Kindle sales numbers:

I'm not sure we will ever reveal all the numbers. Our point of view is that there is a competitive advantage to keeping the numbers close. You may have to remain curious on that point and I certainly understand the curiosity, especially since I look at the numbers so avidly every morning.

With Amazon rolling out Kindle 2 and the Kindle DX in quick succession this year, some customers who bought a Kindle 2 have wondered how they can upgrade to the newer DX. One audience member Bezos asked directly about that. He responded with a piece of advice:

Whenever we have a new device, give your old device to somebody and buy the new device. I heartily recommend it. We have an active and thriving market. You can sell a used device as a third party seller on Amazon.

During his presentation, Bezos said Amazon is "investing very heavily" in its digital business in general, but said, "I don't want people to think it’s a big cash flow generator for us." He said Amazon is also in "investment mode" with its China retail business and cloud-computing:

We continue to plant these seeds and our experience – if something is successful, it seems to be 5 to 7 or more years before it’s a meaningful positive contributor to the economics. Of course it can be a negative contributor much earlier.

Bezos noted that the recent live internet broadcast of an elephant birth in Belgium was supported by Amazon's EC2 compute service. He said the event, which required the equivalent of 175 servers for a brief period, illustrated the value of Amazon's cloud.

"You could never do this with a traditional compute model," he said.

Bezos highlighted the recent explosion of interest in a cheesy black T-shirt sold on Amazon. The shirt, which features three wolves howling at the moon, has sparked hundreds of fawning and over-the-top reviews, some of which Bezos read aloud (Sample: "Unfortunately, I already had this picture tattooed on my chest.")

Bezos said Amazon had no interest in discouraging such viral events.

"We do not delete funny reviews," he said. "This shirt did for a short period of time become the number one bestseller in our apparel store." He then tossed one of the T-shirts into the crowd.

In a later Q&A with reporters, Bezos was asked about Kindle competitors, including the rumored Apple tablet. He said, "This is going to be a big business and there are going to be multiple players and multiple winners," adding, "We want to have the best customer experience."

Asked about Amazon's strong performance so far in the recession, and whether it marks a turning point for Amazon, Bezos said, "I don't think we know. Ask me in 10 years." 

But he did talk a bit about how the economy is affecting Amazon's business, saying that the growth rate for more expensive items in the $500-$1,000 and above range "have slowed according to their historical norms."

"I think people are being cautious about high price point items," he said.