Pros
Huge company involved in nearly every aspect of computer technology so lots of opportunity to get into other groups and work on interesting stuff. Stable, cash rich company means some safety in troubled economy.
Cons
Microsoft is a great company on paper but the work environment here suffers from certain negatives. I find the management to be very passive aggressive in a real mess-with-your-mind kind of way. This envrionment is also WAY more highly political than any I have experienced. (My experience is primarly from large finance, this is my first true tech company). Both factors seem to be institutionalized. I am not convinced Microsoft will be able to continue to compete after next 5-10 years. I feel like we may be at the beginning of a long slow decline.