Vantaggi
Microsoft employs some of the world's smartest people. I've been with the company for 8 years and I routinely learn something new from my colleagues every day. We work on projects that are important to 100's of millions of people around the world, if you want to be part of something that has world-wide impact, this is the place to do it. We have fun, every team has a morale budget for parties and such, and we very casual. Most people have their own offices, though seating is based on time with the company so new hires might double up depending on the group. We have the Gold Standard for health benefits, you'll never pay a dime out-of-pocket for any health care.
Svantaggi
You are guaranteed to get asked to help troubleshoot every Windows or Office problem your family and friends encounter, and it doesn't matter if your job has nothing to do with those products. You get teased by family and friends about working for a monopoly and about Bill Gates' hair, you get to hear about how Linux is so superior to Windows for all sorts of obscure tasks, and people send you links to those damn "Hi, I'm a Mac" commercials. Working in the Redmond, WA area means that 40,000 of your neighbors are also your co-workers, many neighborhoods are easily 60%+ Microsofties, so it can get a bit weird constantly being surrounded by the people you work with.