Pros
At Microsoft you get to work with really smart people. In addtion it is a truly diverse workplace. I have colleagues from Russia, Denmark, Columbia, and Poland working wth me. It is super to have people from different backgrounds and slightly different perspectives, working together. Third Microsoft is the only company that is involved in so many different technology related businesses, and looking to solve a broad span of difficult technology problems. This allows one to follow their passions without having to change employers. Finally although on the outside Microsoft is percived as arrogant, and a monopolist, from the inside, the atmosphere is different. It is more of an underdog mentatliy.
Cons
There are several big downsides to the Company. First it takes time to get things done at Microsoft, and there is quite a lot of unnecessary processes. This is a combination of the size and scope of the company and a result of the DOJ consent decree. Second, while the company is filled with smart people they are not all necessry working towards the same goal and thus 1+ 1 does not equal 2, but instead less than 2. Third, time can fly by while working at MS. Product release can take upto 3+ years, and in this time you may not get promoted. (often promotions are linked to shipping). Thus at the end you may find that you career has not moved very far. Fourth, the company is known for reorganisations. Again this maybe necessary for a company of the size of Microsoft, but it can be a huge distraction, as everytime there is new leadership, you have to schedule reviews, and change the plan fo record. Finally the recent round of layoffs' are going to cause some fundamental changes in the culture at Microsoft. It will become even more political with every person for themselves, and employees spending energy making sure that they look good in the eyes of their managers/VP's.