Pros
Microsoft offers some of the best opportunities in the industry for personal and professional advancement. There is quite simply no other company in the world that will offer you the resources to grow to as deep of a technical level. Community involvement in the form of blogging, attending industry events, presenting, and even time for charity work are all highly encouraged. The medical benefits are the best of any US company, hands down - I have never paid a penny for any clinic or hospital visit, including when my child was born. Management tends to be fairly hands-off in support as long as you are producing and competent. Compensation is excellent with generous stock awards and occassional cash bonuses. Yearly salary increases can be close to double-digits for high performers.
Cons
The things that make Microsoft such a good fit for some make it extremely stressful for others. You will be expected to guide your own career and to be responsible for much of your own learning. This means that you'll probably always be reading up on something and will always feel a littel behind. You'll never acheive a comfort zone in terms of career growth. The environment is competetive, and laid back types who just want to "come in and do my job" will be limited in how far they can advance. Travel is required. Working with outsourcers overseas can be stressful and unrewarding because there is no mentoring relationship to speak of - you will be dealing with lowest common denominator individuals overseas who have no incentive to learn or better themselves because the people back in the States can always get them out of a bind. Support tends to be underfunded, and you will not have all of the benefits that people in the Redmond campus have (but you won't pay $500K for a shabby house an hour away from work, either).