Vantaggi
You can find a wide range of jobs spanning the company, including overseas (if you're willing to switch to a subsidiary). Great benefits (although health will be much less than what it is today come the end of FY13 (July 2012 to June 2013). Some very smart people around and cool products (based on a wide variety of tastes).
Svantaggi
Getting reorged. In my particular case I was reorged more than 16 times in 6 years. Not in itself a wonderful thing, but in the past two years I was reorged enough times where I was doing something completely different every six months. And the way Microsoft works, you are calibrated against your discipline and if you've been doing something well for a year you'll nearly always trump four months of good work. And not gaining in your job level of a certain window of time will damage your long-term prospects.