On Tuesday, , citing an unnamed source, said that Apple's European arm was training new staff to answer queries about Mountain Lion. In the past, Apple has limited the training window, possibly to avoid leaks from the new staff about undisclosed features.

AppleInsider speculated that the staff hiring and training may mean Apple will debut Mountain Lion at its Worldwide Developers Conference (WWDC), which opens June 11 in San Francisco.

The release dates for also may hint at early availability.

Apple has shipped three OS X 10.8 developer-only previews so far, on Feb. 16, March 16 and most recently, April 18.

Those dates are ahead of the schedule Apple set last year when it fed developers a stream of previews for OS X 10.7, aka Lion, which went on sale July 20, 2011.