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Forecasts are all over the place in terms of just how many iPads Apple will sell. The only certain thing is that most everyone has an opinion.

Morgan Stanley is reporting that Apple’s Asian suppliers will ship 8 million to 10 million units in 2010, compared with a previous forecast of more than 5 million units.

And BMO Capital has increased its forecast, too, saying that Apple will sell 2.5 million iPads in fiscal 2010 (which ends Dec. 26). Next year looks even better. The firm raised its forecast for 2011 from 5.5 million to 7.2 million.

Bernstein Research is expecting Apple to sell between 300,000 and 400,000 iPads over its launch weekend, including presales, and sales could go as high as 5 million units in the first 12 months, the firm said. But those initial numbers may be a disappointment to some.

“In the immediate term, iPad expectations appear over-zealous, which could provide a relative short term disappointment for investors,” wrote Toni Sacconaghi, senior analyst at financial analyst firm Bernstein Research, in a brief report previewing Apple’s April 3 release of its highly anticipated iPad. That said, he believes that the iPad could “evolve meaningfully over time.”

Bernstein Research bases its forecast of iPad sales on an analysis of first-year sales for what it considers comparable successful products such as the iPod, Kindle, PalmPilot and AppleTV.

“Each of them sold less than one million units in year one,” Sacconaghi wrote. “Moreover, even extensions of clearly defined categories such as the iPhone (6.1 million), iPod Touch (about 6 million) and netbooks (8.8 million from all vendors) sold less than 9 million units in year one.”

The report further noted that the iPhone’s historical sales trajectories showed daily sales over launch weekend being four to nine times higher than the daily run rate over the remainder of the first year.

A recently released survey of consumer attitudes regarding the Apple iPad and plans to purchase it showed that while interest was very high, only about 10 percent of both existing Apple device owners and non-Apple device owners said they would shell out the cash for an iPad in the next six months.