Pros
Good benefits, although they get nipped back a bit every year. Vacation accrual is fantastic. 90 percent of admin positions are hourly, and can often be as much overtime as you'd like to work. The role is very broad: you can dabble in a lot of disciplines. The company values have gentled over time to emphasize happier, healthier employees who don't feel worked to death. Real commitment to good corporate citizenship. As a company, very much likes to promote from within.
Cons
Admins are just not getting the comp packages they deserve. Pay stalls hard in the 56-57 bands. You must be part of a two-income household to even pay rent, much less own, as a Microsoft admin. You are not bonus eligible. Raises run around 2-3 percent, which can be less than a rent payment. It is a very broad position, depending on your manager. You clean offices for new hires, set up new PCs, negotiate for office space, may manage budgets. Responsibilities merge with the much more highly paid Business Manager position which can be very hard to get (and will always be underlevelled for an admin making the jump). Even at the VP and sometimes at the CVP level, you will be responsible for multiple calendars, with no real diminishment in group admin expectations.