Microsoft CEO Steve Ballmer has confirmed here at the BUILD 2012 developer keynote that since Friday, the official launch of Windows 8, the company has already sold four million Windows 8 software upgrades.

That's certainly not a bad start for Windows 8 but at the same time, most people will likely still stick with their current Windows OS and wait to buy a new PC to get Windows 8. On that front, Ballmer says that sales of Windows 8 products are good so far.