In a parallel universe: Gates returns, fires Ballmer and turns MS around. Reality: He's probably happier solving much bigger problems in the world. But still, it sucks to see someone drive his company to the ground. Has Ballmer ever done anything right for Microsoft? I can't think of anything.
He's kept the ship afloat and is good at maximizing profits from MS's traditional businesses. The problem is that Ballmer isn't the person you need in a transitional phase for a company.
Remember when they haven't shipped a web browser in Windows 95 and then they turned around and produced a kickass browser that killed Netscape Navigator? Or how MS Word took marketshare from WordPerfect like taking candy from a baby? Or how Win 95 won against IBM's OS/2, even though OS/2 was also binary compatible with DOS and Win3.11?