In contrast to all of Microsoft's rivals: IBM left the PC Business. Sun literally died and got bought out. Oracle's products were eaten alive by Open Source.
Under Balmer, Windows 7, XBox and XBox 360, Kinect. Do remember that Windows Mobile 6 was a major competitor vs Blackberry through the early 2000s.
Ballmer tripped up in his final years with Windows8 and failing to bring the success of Windows Mobile 6 to post-iPhone markets. But I think he did good from 2001 through 2011 overall.