But Microsoft's biggest threat to Windows OS growth, says Rosoff, is the idea that existing . "Consumers and businesses may have no incentive to replace them until they break," he says.

Apple Clout May Increase with New OS

Veteran industry analyst Roger Kay, president of Endpoint Technologies, says he doesn't see Linux as a threat to Microsoft now or any time in the future, and says it would be a mistake for Microsoft to take its eye off Apple.

"Apple can move as a unit. The Linux crowd can't," Kay says. "Linux is just a collection of philosophically aligned developers without a well-financed backer. I'd be much more leery of Apple, a company with [US]$25 billion in cash and a crack team of technologists and marketeers."

Likewise, Tim Bajarin, president of tech consulting firm Creative Strategies, says that Microsoft is in no position to take Apple lightly. He believes Apple has the superior client OS, but that Windows 7 is a big improvement over Vista and should help Microsoft keep their market share steady.