Pros
If you find the right manager and the right group, it's possible to go far. The benefits are stellar, with no co-pays on anything. We get stock grants instead of options, so that's just an extra cash gift (albeit one that pays out over five years). There are lots of challenges to be had in the company, and it's not too hard to carve out your own niche and really shine. If you don't like what you're currently doing now, there's a lot of opportunity to try out something new -- even changing disciplines if that's what you like. Name any pair of disciplines, and I can show you an example of someone who switched between those two disciplines.
Cons
If you have a bad manager or are in the wrong group, it's next to impossible to level. When you tell someone you work for Microsoft, you get to hear their litany of complaints about any Microsoft product that they've ever owned and that didn't shine their shoes for them.