Pros
Location, location, location. If you live in the Puget Sound area (namely Seattle), are Software professional, and want to work for a Software company, there are few alternatives. The software business of the Puget Sound is Microsoft. Microsoft offers the most career choices, the most opportunities, the best benefits... in the Puget Sound area. Compared to the Silicon Valley companies, Microsoft is decidedly average, but the Puget Sound area is not Silicon Valley. Microsoft does employ some of the world's brightest people, and the line of applicants at its door is looong, but the brightest people don't make for the world's best company.
Cons
I was forewarned on my very first day: beware of politics. Microsoft is politics. Every decision is a political decision. Everyone treads lightly for fear of lawsuits. The unofficial company motto might be: "Do The Right Thing" (TM), but --in truth-- it's more of a "For the Love of Bill, Whatever You Do, Don't Do The Wrong Thing." The decisions which do get made are the safe, conservative, politically correct, decisions. Innovation is always constrained by the Big Fear: the fear of lawsuits. Every discussion seems to be chaperoned by somebody from LCA (Legal Compliance) and no matter how important you are, how smart you are, how right you might be, the LCA is more important, more right. The very bright people (TM) employed by Microsoft are constantly hamstrung by lawyers, by the esprit d' conservatism, and by the egos of the million other bright people working there along side of them. Microsoft is like the proverbial Old Boys Club: everybody who is anybody has been there since the beginning of time. To get your foot in the door at Microsoft is tough... to lose your job for any reason is even tougher... as long as you don't do The Wrong Thing. It's easier to keep quiet, do your job, and not question things. Questioning is definitely a Wrong Thing. Especially if you haven't been at Microsoft since the beginning of time. About 25% of people on the Redmond campus aren't even Microsoft employees: they are contractors (aka: "Orange Badges"). And Orange Badges, even if they otherwise qualify as Very Smart People" are treated not like second-class citizens: they are necessary and tolerated, but resented for their paychecks. Orange Badges are supposed to do their job. Otherwise they should act the part of a good butler: silent, halpful, invisible.