Microsoft may not have pointed out the specific difference that netbooks made to its Windows business last quarter, but the numbers were there. "We found a continued deterioration in the PC market," said Koefoed, who added that by Microsoft's estimates, global PC sales declined between 7% and 9%. Its unit sales for Windows tracked that closely -- down 6%, said Koefoed -- not surprising, since most machines sold come with Windows preinstalled.

In pre-netbook days, Microsoft's Windows revenues were more-or-less in sync with PC sales, Chris Liddell, the company's chief financial officer, noted as he answered a question later in the on Thursday. In other words, if PC sales rose 8% during a quarter, Windows revenues grew by about the same amount. But netbooks have thrown a wrench into that calculation, Liddell acknowledged, making it difficult to predict future Windows revenues.

Allan Krans, an analyst with Technology Business Research Inc., put it more bluntly. "That's what got Microsoft from the 6% decline [in Windows unit sales] to the 15% to 16% decline in Windows revenues," said Krans. "Netbooks are a growing impact on Microsoft's bottom line."

Netbooks can't take all the blame for the drop in Windows revenues, Krans cautioned -- the larger issue is the -- but they exacerbate Microsoft's problem. And it's not going to get better overnight, if ever.

"Netbooks, and lower-priced PCs in general, show a fundamental shift in buying," Krans argued. "It's not something that will go back to the way it was any time soon. The shift is away from bigger and better toward simplicity and ease-of-use." The latter, he said, was one reason that , even though its Macs are premium-priced. "People want something that's easy to use, not heavy and complex," said Krans, referring to operating systems.