As noted by Macworld UK, Apple's OS X Mountain Lion has clawed its way to the top of the OS X jungle. It was released on July 25, 2012 and as of this past December it's installed on 32 percent of all Macs online. That percentage is according to Net Applications, a web-measurement firm that tracks operating system usage by analyzing visitors to 40,000 websites.
That number represents a 3 percent increase for the OS from November, when 10.8 was running on 29 percent of all Macs online. That gain came mostly at the expense of OS X 10.7 Lion, which sank from 30 percent to 28 percent. Mountain Lion also stole one percentage point from OS X 10.6 Snow Leopard, which is now actually in second place, accounting for 29 percent of all Macs.
Interestingly, Computerworld has compared Snow Leopard to Windows XP, noting its strong staying power. They attribute this to the stability of the OS and the ability of Snow Leopard to run PowerPC apps.
Net Applications doesn't expect any future Mac operating system to ever crack a 50 percent share. That's due to Apple's new annual OS X update cycle. If OS X 10.7 and 10.8 are any indication, Apple should announce the 10.9 beta some time this spring with the official release coming in July.
Apple Mac OS X Lion
Apple OS X Mountain Lion
Apple OS X Yosemite