Pros
Resources a mile wide and a mile deep. Microsoft has lots of money and is committed to spending in on its people. So compensation is excellent, benefits are out of the world, and you'll have everything you need in terms of hardware, software, and staffing. As a result, they attract the best people in the world, which is the best resource of all. You will never find smarter people or better managers.
Cons
It seems like everyone on the outside hates Microsoft, which can make it a little demoralizing to work there. It is a large company, and even though it is broken up into usefully small groups there is a vast bureaucracy. Government interference means even more bureaucracy - protocols need to be documented, emails need to be retained (and carefully composed). And Microsoft as a company has no taste, as Steve Jobs once pointed out, which means they make stupid errors about products. That's an uphill battle.