This is big news. Microsoft has been making some massive changes over the last several months without a successor to Steve Ballmer in place (like its re-org, purchasing Nokia, etc.), which is more than a little disconcerting, so the sooner they have a CEO nailed down, the better. And Nadella has been heading up one of the most successful units at Microsoft, so perhaps he’s a good candidate for the job. He’s certainly going to have his work cut out for him.