Had one 1-1 interview on campus and then heard back from them two weeks later that I had a second round. They flew me out to the Corporate HQ in Redmond, WA (placed us in the Westin, really swanky, with everything paid for by Microsoft -- including food, taxis, flight, etc.) and had one Super Day that consisted of 4 interviews with various senior managers. During the Superday, they gave us a tour of the campus and in the evening we had a social at a bar/lounge. Heard back from them the next week and got an offer. Overall process was fair and enjoyable, and it wasn't too stressful.