Vantaggi
Good health benefits are available for everyone at Microsoft. In the Seattle/Redmond area you get a health club membership, or can opt for $800/year in reimbursed expenses. Need a new bicycle to workout? Use it for that. Microsoft has been good on resumes for getting interviews at my new company, however most experience Microsoft engineers fail their interview because the work at Microsoft doesn't prepare them well to get hired outside. You have to do that yourself.
Svantaggi
Your work at Microsoft prepares you to do your job at Microsoft, not a lot on the outside. Every year someone would get the bad annual review, which meant everybody is on edge for the rest of the year. What does that mean? Their is incentive for your coworkers to stab you in the back. Managers don't know much about your daily work, so presentation skills are vital to get the visibility you need to survive. No matter how much Microsoft wants you to have work-life balance, everyone ends up sacrificing it due to the threat of a bad review. That doesn't mean your boss wants to skewer you (he/she might; different story), it means everything is tinged with internal competition. Internal competition is more important than external, because the customers won't fire you, but your boss will.