Mine was an internal interview loop that lasted two days, two directors, two technical managers, hiring manager, peer, and GM. Microsoft tends to have what's called an AA (As Appropriate), which is when you know you're a serious contender. Many people never make it to the AA. I had to send some emails to follow-up, but otherwise the process was thorough and professional. I must have been runner-up because they kept me on hold longer than they had initially noted.