Pros
For people just starting their careers Microsoft is an amazing place to gain experience. You will be involved with decision making and building products with huge reach. The workplace is a highly energetic one, where everyone is focused on one thing primarily, how to ship great software and products. You will learn as much about the business of software as you will about actually building it. To thrive in this environment you really need to be passionate about your work and the products you'll help build. You will be working with some of the highest caliber people in the industry and expect to be challenged when just starting out like you have never been challenged. You will start with little responsibility and will need to prove yourself to take on bigger pieces. In my opinion, the people you will collaborate with and learn from is one of the most valuable things you will gain by working at Microsoft.
Cons
The environment is filled with an unnatural distribution of highly intelligent and passionate people and is very charged. It's not uncommon to hear full on yelling when there are disagreements. In fact this is almost part of the Microsoft culture. This certainly varies from team to team, the older more established teams following this pattern more closely. This can take a little getting used to depending on where you're coming from. Every team has it's own culture for how they reward their employees and how they're centered. Dev centered organizations place the most value around the output of developers writting the product code. Other orgs are more equally balanced between value placed on dev, test and PM.