Vice President of Mac Software Craig Federighi just revealed during the Worldwide Developers Conference opening keynote that Lion is the fastest selling version of OS X for Apple by selling 26 million copies in only nine months. He was also quick to note that it has better adoption than Windows 7; with over 40 percent of Mac users currently on the new OS X. Apple also gave us a look at how many Mac users are in the wild, which now totals a whopping 66 million.