Vantaggi
If you're a fan of Microsoft products, there's no better place to use the latest technology. Depending on your group, you may be using products that aren't even available to the general public. There isn't a single best way of doing things at Microsoft so each organization is free to develop their own best practices. From a career perspective, changing groups is like changing companies without having to start earning vacation again. The privacy policies are top notch. I have a lot of faith in my employer doing the right thing with a customer's personal data (even when I'm the customer) because I've been a part of so many reviews where privacy is highlighted as one of the most important things.
Svantaggi
Too many fiefdoms: Microsoft was once a place where the best technical solution would win the day. There was time to argue the best way of implementing a feature. There are some important people around with delicate egos. Say the wrong thing and they will go out of their way to put in a bad word at review time. Easy to get stuck in the wrong role: I've witnessed people getting dropped in the wrong role after a reorganization. If you haven't been in your current role for 12-18 months, you could get stuck in an area that's outside your specialization. Come review time, that could mean a black mark on your review or the end of your job.