Vantaggi
The opportunity to pursue your work interests outside your core job. Even if your job is to simple write the code for a single button in Excel, you can still follow other interests at Microsoft. You can many opportunities to get outside of your box. There are so many different groups and so many different types of work to do at Microsoft that, if you can't find something to suit your interests or further your career, the problem is with you-- not Microsoft. The benefits are also incredible, anything from deals with local retailers, to gold-level membership with Fidelity.com and other services.
Svantaggi
The primary downside of Microsoft is that a lot of the old-school people from the early days of Microsoft are still hanging on at Microsoft and not moving on or retiring. This limits the ability for talented people with new ideas from taking on senior positions. One of the other downsides is that the jobs, whatever they are, aren't exciting in and of themselves-- as an employee, however, you can take many different steps to expand your possibilities, challenges, and abilities. Another downside of Microsoft is the review process; while heavily instrumented, the instrumentation is highly subjective and I've never met a manager (or employee) that fully understands it.