From gamasutra.com:

Greenberg is very bullish on Kinect, predicting three million sales this holiday season, globally.

"Our key indicators are feedback from retailers -- I think you'd be surprised at how sophisticated they are, and they really have the pulse of the market. They're looking at preorders, they're talking to customers.

"We're also done our own research. We believe this will be the biggest launch in our history, for Xbox. We will sell more Kinect sensors than we did [systems] at Xbox 360 launch."

"Our estimates that we will sell in excess of 3 million units this holiday," The company is spending "hundreds of millions" of dollars in marketing, "exceeding in what we did when we launched the original Xbox 360," says Greenberg.

The generation, at this rate, seems to be tracking longer. Of course Sony has always talked about a 10-year cycle, but so does Greenberg. "We do think that this generation is unique. We're treating the launch of Kinect as an entirely new platform launch, as almost a new generation. For us that does extend the product life cycle."
At this point in the Xbox 360's lifespan, he says, "we're five years in. We think we have another good five years-plus, but that remains to be seen -- but easily there's another five years' life."
Full Story: gamasutra.com