Pros
Microsoft is still a very powerful company. There are jobs and software it creates for just about everything. You feel like the company cares about you, far more than free soda. They have training classes on everything you could think of, and for those who manage to get themselves into the good graces of management who likes them, the sky is the limit. There are still good jobs at Microsoft, but it's hard to find them.
Cons
There is a strong tradition of failing upwards. The company has lost a lot of its best and brightest to other companies, and the bottom-feeders that are left tend to be very bad at their jobs. The company's biggest problem is how political it is. You will never get a promotion on the merits of the job you do, you must get into the "inner circle" of a higher-up manager to have any chance. Most of the time, instead of dealing with the politics, people just get fed up and leave -- and forever after have nightmares about their experience. The company has a mandate to fire 7% of their employees a year, and if you aren't in the top-tier inner circle, you feel like you're always fighting for your job. Every promotion you get is one that someone else did not. Avoid the Office division like the plague, it is the least innovative part of the company. The technical stagnation of "It's been done this way for years, and we'll continue to do it this way" permeates every part of the product. You will not grow or learn there. For some, it's OK because they have a relatively high paying job that doesn't expect much of them. But I wanted more.