Pros
Great stability, competitive or high salary, great benefits. Lots of smart people. Many opportunities for professional development both internally and externally.
Cons
Hyper-competitive, stressful working environment, larger groups are extremely political. If you get a bad manager, you're sunk because HR will support Microsoft managers no matter what. And make no mistake, there are plenty of bad managers, most of whom were promoted into their position because of individual excellence but who have no idea how to motivate or develop people. Microsoft says it values respectful communication but many managers get away with bullying and intimidation without repercussion, because upper managers don't even know it's happening. There is a HUGE over-reliance on e-mail and instant messaging, leading to frequent miscommunication and strained relationships.