Tim Cook has just announced that 28 million copies of Mountain Lion have been shipped to date, making it the best-selling OS X ever. The Mac now has a user base of 72 million people, and 35 percent of these Mac users are running OS X 10.8. "The Mac business has out-paced the PC business for several years now," said Apple CEO Tim Cook, making the MacBook the No. 1 US notebook and the iMac the No. 1 US desktop.