Pros
Ability to move around different roles, projects, groups, jobs. Microsoft has so many projects and business groups that one can easily find a job or role that you like. There are also many bright people at Microsoft that you can learn from. Benefits at Microsoft are also top notch, especially for those with families. The company also is fairly flexible with work life balance and gives employees a lot of freedom to set their own schedule. In other words, there is very little micro management done at Microsoft and the attitude is more along the lines of manage your own schedule, just make sure what needs to get done gets done.
Cons
There are many layers of management, sometimes too many. You can get bogged down with meetings upon meetings in order to get buy off from all management levels. Not only does this slow the generation of new ideas, but it also becomes a drag on productivity as many times you will feel like your job's many purpose is to prepare for a meeting. And because this is a large company with many business groups, office politics and fiefdom creation can become prevalent. Finally, there does not seem to be much accountability at the management level so bad decisions often go un-punished.