Pros
I had a really good team. The people I worked with were very talented (and in some cases borderline genius) and opinionated (in a good way). It's a great place to start your career and you will learn a lot (both good and bad). It's also such a huge company so you can change teams internally and do something very different. And pretty much you will find all sorts of people in the company. For every employee that you think is unworthy, you'll find 10 others who make it great. And the compensation and benefits are basically second to none (even with the changes to the health care plans). Work life balance is so much better at MS than at a startup.
Cons
Being a huge company some bad apples somehow find its way though and they coast along despite the horrid stack ranking policy (another con). And dealing with them is tough unless you have a great manager. Culture wise, I found that a lot of people tend to "drink the kool-aid" as it were. They don't want to try competitor's product and will love everything MS puts out. Which can get irritating when you're trying to point out a valid flaw (or explain why a lot of customers may not like a feature) and explain why it should be fixed.