Mountain Lion's trio of previews were 8, 15 and 25 days earlier than the first three Lion previews: The former is now more than three weeks ahead of the latter's 2011 timetable.

If Apple keeps to the established pace and seeds one more preview to developers -- Lion offered four last year, then a so-called "gold master" build before hitting the Mac App Store -- Mountain Lion would go on sale June 25, with the gold master ready June 6.

That last date may be a tad early, as Apple opens WWDC the following week. It seems improbable that the company would preempt a ready-for-sale announcement at WWDC by releasing a gold master of OS X 10.8 several days earlier, entailing a risk that the news would leak.

Also in play are expected refreshes of Apple's computers.

Most experts assume Apple will unveil new iMac desktops and MacBook Pro and MacBook Air laptops this quarter and next with Intel's Ivy Bridge architecture. Ivy Bridge is Intel's third-generation design of the Core clan, and the first to use a 22-nanometer manufacturing process.