Mac users are nearly three times more likely to be running an early version of the OS X Mountain Lion operating system than PC owners testing Microsoft's Windows 8, the Chitika online ad network said today.

During a week following Mountain Lion's release, its share of the Macs that accessed Chitika's network was a puny 0.06%, or six out of every 10,000 Macs.

But that was nearly three times the percentage of Windows users running Windows 8 who were served an ad in the early days of that operating system's availability. In the same period following the release last September of Windows 8 Developer Preview, just 0.021% of all Windows PCs were powered by that sneak peek. (The number represented 2.1 PCs out of every 10,000 running one Windows flavor or another.)

Chitika regularly mines its ad impression data for trends in operating system and browser usage patterns.

Apple released a developer-only preview of Mountain Lion, otherwise known as OS X 10.8, on Feb. 16. Microsoft launched its Windows 8 Developer Preview on Sept. 13, 2011.

Since that second date, Microsoft has also shipped Windows 8 Consumer Preview, a more polished version of the build it distributed last year.

The two companies took different tacks to distribute the first versions of their next desktop operating systems: Microsoft allowed anyone to download the Windows 8 preview free of charge, while Apple limited Mountain Lion to registered Apple developers, people who had paid a $99 annual fee to receive early Apple code.

While Microsoft boasted last year that three million copies of Windows 8 Developer Preview had been download between Sept. 13 and Dec. 7, 2011, Apple has not divulged the number of developers who downloaded Mountain Lion's preview.

The percentage of users running a preview may be in Apple's favor, but Microsoft has the clear advantage in sheer numbers, since Apple's global usage share is only 7% to 8% of all personal computers, while Windows' is between 90% and 92%.

According to Chitika, more Mac users are still running Mac OS X 10.6, aka Snow Leopard, which accounted for 47.5% of all Macs. OS X 10.7, or Lion, garnered a 30.5% share.

Those numbers were similar to the ones published by Internet metrics company Net Applications earlier this month. Net Applications had Snow Leopard accounting for 43.4% of the Mac OS X market during February, with Lion at 38.9%.

Chitika cautioned that it's dangerous to read too much into the small percentages of users running the previews.

"Low levels of use for unreleased versions of software are typical ... given that in the early stages of a product, the heaviest users tend to be developers who are focusing on testing and preparation of the release," the company said in an email.

Apple is expected to ship the final edition of Mountain Lion late this summer. Microsoft has not disclosed a release date, or even month, for Windows 8, but most analysts have pegged that to October 2012.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed . His email address is gkeizer@computerworld.com.

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