Pros
Great growth opportunities, the greatest software company overall, great pay and benefits, great choice of things to do at work, working on world class software, working from home is not a problem, flexible hours have the positive meaning... Even if you decide to leave the company - this is great for your resume. You learn a lot at Microsoft with the challanges of satisfying millions if not billions of users with your work every day. You work with some of the greatest engineers in the world, with people who are smart and friendly. Then there's free drinks, Starbucks and pizza almost every day, sports club membership and many social events! :)
Cons
Working far from home is a must if you were not born in Seattle and want to develop the biggest products. Many customers do not like Microsoft, so you have to explain to people you are not working for an Evil Empire. It rains a lot in Redmond too! Advancing the career might be slower than in startups because of great competition, but it is almost guaranteed as opposed to startups, which often fail. Sometimes it is easy to get lost in such a big place. Sometimes you might feel like a little cogwheel in a huge machine, although everyone is important and you can always try to grow and become a big one too!