Give up Yahoo and clean out Windows Live/MSN. Too much crap that's not yielding any results.
Pros
By far the biggest benefit for me is the opportunity to work with peers who really are the best and the brightest. At previous companies I have worked at, I would frequently get frustrated with the level of incompetence of others i had to work with. With very few exceptions, most everyone at MS has a right to be there. I can't say enough about the opportunity to transfer across divisions and disciplines if you are motivated to do so. Work/life balance goes in cycles, but in general is ok.
Cons
Bureaucratic bloat has impacted the ability for most teams to be agile. For a technology company, it's amazing that there is almost no acceptace of remote/virtual work. While working remote/telecomutting, part time, etc is given alot of lip service it's almost always career limiting.