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 .

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at , on or subscribe to . His email address is .

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