Lion's share line will probably begin to resemble the one seen here for Snow Leopard, the OS X that has slipped since 10.7's debut in July 2011. (Data: Net Applications.)

Along with Snow Leopard, which last month had a 40% share of all OS X systems, the vast bulk of Macs in use -- 84% -- may be eligible for the upgrade to Mountain Lion.

Apple accelerated the abandonment of OS X 10.5, or Leopard, in April when it began to Snow Leopard to users of who were still on the older OS. In April and May, Leopard use dropped from 13.6% of all Macs to 12.3%.

Although those free upgrades were intended primarily to prepare Macs for the June 30 disappearance of MobileMe -- that deadline is when the newer iCloud online sync and backup service becomes Apple's sole cloud offering -- it also made some of the machines able to qualify for the Mountain Lion upgrade.

Many of the features that Federighi demonstrated today were ones that have been leaked since the February 2012 release of the first Mountain Lion developer preview, but scores of others had not been widely discussed, including system-wide sharing of photos, videos and other files; future integration with Facebook; an OS X version of Game Center, Apple's under-utilized multi-player gaming portal; and voice-to-text dictation from within any application that accepts text input.