Pros
First, Microsoft is a giant in the tech industry - everyone either works with or competes with Microsoft in some form. As such it is a great nexus to be in to be part of the sweeping changes in the industry. Microsoft may not always come out top (at first), but you will be part of the mobile transformation, online services, gaming, software as a service, voice over IP and more. That's a great feeling. Second, Microsoft is a large company where moves are pretty easy. I moved from Corporate Strategy, to Business Development, to Product Marketing in Consumer Online Services then to Product Management in Enterprise Servers. Next move will likely be a stint in the field, probably in Asia. The chance to get these experiences is awesome. Finally, Microsoft is over the "get rich on stock options days". People are a lot more sensible about base pay, bonus, stock awards, benefits as a whole package. You may not get filthy rich quickly at Microsoft, but you will have a much more stable and comfortable overall life.
Cons
Fisrt, Microsoft competes in so many areas, that it feels like we are always playing catch up to more nimble competitors. This can be disheartening and challenging at the same time, and it definitely takes a lot of energy to keep pushing. Second, Microsoft still has a lot of old guard in place at the top and it sometimes feels like "Ballmers old boys rule the roost". But, that is clearly changing as more outsiders are brought in at senior levels of the company. Third, Microsoft does best on big bets that require an amazing level of coordination between field, development, marketing, PR and so on. The doenside is that it can lose the entrepreneurial feel.