Though everyone knew it would come eventually, especially with figureheads like Steve Ballmer at the forefront, the Chairman of Microsoft, Bill Gates, will be stepping down more or less to focus on his charity foundation. While he will be still Chairman, the majority of his duties will be taken over by others. A company the size of Microsoft can often be self-perpetuating, but as one of the youngest software giants (compared to, say, IBM), a change in leadership can have dramatic results on the way a company functions. He isn't concerned, of course:

”This was a hard decision for me,” Gates added. “I’m very lucky to have two passions that I feel are so important and so challenging. As I prepare for this change, I firmly believe the road ahead for Microsoft is as bright as ever.”
Gates job must be a lot more complicated than it would seem on paper, as they've planned out a 2-year transition period for others to assimilate his duties. Will this impact Microsoft in the long run? Probably not, and it does seem that Ballmer has already been spearheading many of Microsoft's endeavors. You can read the full press release at Microsof't site.