Pros
The best thing about working at Microsoft is that you get to work with a lot of extremely intelligent and passionate people. At the time I didn't put a lot of weight into that, but now that I'm working at a company where people are just punching the clock, I realize how invaluable that was. There are a lot of politics in decision making, but if you learn how to deal with the politics then it is manageable and your career can grow to all new heights.
Cons
My main con is that Microsoft's main location is in the Seattle area. Which if you are willing to relocate, then this is actually a pro because its a great place to live. However, for people like me who want to stay close to their family, then there are limited choices for development offices. There are offices in Boston and Raleigh, but they are small and tough to get into.