Pros
Microsoft's medical and dental benefits are great. I think they're probably the best I've experienced, having worked for a number of large high tech companies. It's a large company that has a relatively good reputation, especially outside of the IT industry. Its big name will help open a lot of doors to other employers.
Cons
If you get tired of references to "the evil empire", don't work at Microsoft. While the company might have a relatively good reputation outside of the IT industry, there are a lot of people who have negative opinions of the company because of their past business practices. The stock hasn't done very well over the last 7 years, either. Microsoft certainly isn't a place where you can "rest & vest" anymore. If you're looking to make money on stock, this isn't the place. The salary portion of the compensation isn't bad, but it isn't great. Microsoft pays a little below the market, from what I've seen in the salary surveys.