"Ballmer doing a great job on stage," tweeted Patrick Moorhead, principal analyst at Moor Insights & Strategy, from the event.

Microsoft's CEO was easily the most energetic of the four speakers the company put on stage today, speaking clearly, sometimes quickly, about what he saw as the strengths of the new operating system.

"This leaves no doubt that Windows 8 shatters the perception of what a PC really is," Ballmer said. "One device now pairs the greatest qualities of the PC and the greatest qualities of the tablet experience. Are these new designs PCs? Yes. Are these new designs tablets? Yes."

He was referring to the many keyboard-equipped tablets and so-called "hybrids" -- systems that combine elements of both a tablet and an ultra-thin notebook -- that Microsoft and its OEM partners are introducing alongside Windows 8 and Windows RT.

Before Ballmer's moments on stage, Sinofsky kicked things off with a recap of Windows 7's success, reiterated that the will be available at 12:01 a.m. local time Friday, then took on the tough task of explaining the differences between Windows 8 and Windows RT, something even industry veterans and long-time IT professionals have struggled to digest.