Most of the additions in Mountain Lion had been revealed before today; Apple seeded developers with previews starting last February. But Apple had a few surprises up its sleeve, including built-in dictation, presumably via the same Siri-based technology that debuted in March on the new iPad, and Power Nap, which lets Macs conduct backups and receive updates while in sleep mode.

Power Nap works only on second-generation MacBook Airs and the new Retina-equipped MacBook Pro.

Recognizing the importance of China to its current and future revenue, Apple also added some new China-only features to Mountain Lion, including improved support for Chinese-language input, a new Chinese-language dictionary and support for Baidu, the Chinese search engine.

Federighi said that Mountain Lion would ship in July -- somewhat sooner than many had expected from Apple's "late summer" window of earlier this year -- and will be priced at $19.99, a third less than last year's Lion. Macs running either Snow Leopard or Lion can be upgraded to Mountain Lion.

The disclosure of a release month and the price for the last two OS X releases, when similar information was offered during 2009's and 2011's WWDC keynotes.