Pros
I love working for Microsoft. It's the best job I've had. I'm a high-performer, and have been well compensated for it. I've owned my own company, and have held leadership positions in a variety of different types of orgs and can truly say that, on balance, it's awesome. Smart, talented people. Fantastic benefits. Great to have stock grants versus options (particularly given the market). Good work/life balance especially if you have a family. High degree of freedom to define your role, and manage your own business as a 'field' employee (versus Corporate). If you understand how big organizations work, and know how to navigate them, you'll do well here. Where people fall down is assuming they can change the organization without really understanding how it works first.
Cons
The organization is byzantine. It takes, easily, 6 months to begin to understand the basic breakdown between the different groups. It's also hard to find any one spot where you can understand how all the pieces fit together. This can be extremely frustrating initially, and also makes it difficult to find the people you need to in order to accomplish your goal. Corporate is sometimes slow to respond to either the concerns of the field, or of the customer. Incentives between parts of the organization are sometimes not well aligned. We also tend to be a little too focused on our internal organization versus the needs of the customer.