Internal competition is common at great companies. It can be wisely encouraged to force ideas to compete. The problem comes when the competition becomes uncontrolled and destructive. At Microsoft, it has created a dysfunctional corporate culture in which the big established groups are allowed to prey upon emerging teams, belittle their efforts, compete unfairly against them for resources, and over time hector them out of existence.
"Of course power tools and alcohol don't mix. Everyone knows power tools aren't soluble in alcohol..." -- Crazy Nigel