Two years ago Apple pulled off an impressive feat: Its market cap surged past Microsoft to become the most valuable company in the tech industry.

Then last year, IBM managed to slip past Microsoft to be more valuable. It's since fallen back and Microsoft is more valuable.

Who will it be this year? Well, it could be Google. The search company is just $19 billion behind Microsoft. All it would take is Google's stock going on a tear, and Microsoft's fading or sitting still.

When (or if) it happens, you know Microsoft CEO Steve Ballmer is going to freak out. Don't forget, he's the guy who threw a chair and had a tantrum when Google poached one of his employees.