As of November of 2011, Lion was the third most popular Mac OS, behind Snow Leopard and Leopard, according to Chitika. At that time, 56% of Macs were booted from Snow Leopard, while 16% of Macs were running Lion. More recently, data from Net Applications, which looks at Internet traffic, put the Lion number at 34% in January 2012.
Which means that even among consumers, most Mac users are still running Snow Leopard.
With so many Snow Leopard Macs, there is a question of whether Apple permit Macs running Snow Leopard to skip Lion and upgrade to Mountain Lion. Apple does not enable upgrading from Mac OS X 10.5 Leopard to 10.7 Lion with out first paying for and installing an upgrade to 10.6 Snow Leopard. But the time between the release of Leopard and Lion -- 4 years -- was longer than the 3 years between Snow Leopard and Mountain Lion, a year less time for people to upgrade. In this beta (Developer Preview), Apple is allowing users of Snow Leopard to skip Lion for Mountain Lion.
With Apple trying to merge the user experience for Mac OS X and iOS, Apple may be trying to merge the upgrade rates. Adoption rates are high for major new iOS builds, which now come every year. iOS updates are free, but iTunes keeps bugging you to upgrade every time you plug the device into the computer. This is likely not a feature most IT departments would like to see in Mac OS X, considering the growing number of iPads being purchased by large businesses.
The new functionality in Mountain Lion that Apple announced are focused on consumer features, which Apple says are inspired by iPad. Mountain Lion inlcudes several iOS 5 apps and features, including Reminders, Notification Center, Notes, iMessage (which replaces iChat), and Game Center. The content from these and other features are automatically synced with iOS 5 devices through Apple's iCloud.
Notably missing was Siri, the voice-interfaced artificial intelligence feature of the iPhone 4S. It is possible, however, that Apple is likely to announce more Mountain Lion features during the next few months or at the launch of Mountain Lion.