Pros
Great Benefit, huge career opportunities , variety of people & technologies. You may come across many smart individuals. It's amazing to see depth & breadth of technologies & people they have. Each group/ organization is like company within a company. They have completely different working style, technologies , people skills & possibly evaluation process. Upper management & HR is really working hard to make it a better place to work, but I think they don't realize that real bottleneck is their hierarchy & too many managers. Company with great history & big name, so you can be proud of when you go home.
Cons
Having a bad manager (it often happens) can screw your career & growth at Microsoft. There is a clear lobby in Organizations like Office & Windows. I haven't seen such things in Live/MSN. I would love to work for this company if they get rid off leads & managers who are just playing games, checking emails & giving big management lectures w/o having any technical insight. Too much hiearchy comes in a way for company's progress & decision making process. Also, leads & managers tend to have favorites of their own w/o any specific work related reasons, so if you are not one of them then good luck!!! Also, dont expect much once you have joined this company, bonus & stock awards are peanuts compare to what you can get outside. In short, great place to work for, but filled with tons of bad managers