For those that want to work for Microsoft, the interview process is described over at Carson Critique. I’ve heard that some of the questions are pretty wacky, and try to get you to really think (although there are no right or wrong answers).
They stated to dress casually, as that’s how most Microsoft employees dressed. So instead of suiting up in my jacket and tie, I went with a more casual button up and jeans. As I walked up to my interview location, I noticed a good amount of people were in suits (interviewing with other companies), but my recruiter greeted me sporting a casual attire as well, so all was good.