Microsoft head Steve Ballmer predicts that come 2013, Windows 8 will have amassed a user base of 500 million. The outspoken Ballmer made this optimistic statement during the Seoul Digital Forum, of which he touts Windows 8 as "a dawning of the rebirth of MS Windows." There's no denying Microsoft's strong grip on the OS market in general, but the claim of 500 million users garnered in such a short time span might not convince some folks. Moving to Windows 8 will reportedly be easier on new PCs, as Microsoft is charging only $15 for the upgrade. With Windows 8 eschewing a lot of its predecessors' features such as the Aero Interface and the Start Button, the new OS is set to be quite a departure from Microsoft's previous OS efforts. "It's certainly the most important piece of work we've done," adds Ballmer.