Avantages
Great people to work with, excellent working conditions and a very balanced approach to work-life issues. For example, I was in a mid-level executive position for a while, and decided I wanted to be more of an individual contributor for personal satisfaction and quality of life issues. My boss generously recommended me for the new position, and relationships are good both with the old and new organizations. I've never worked at a place that was willing to go that far to ensure retention of good people.
Inconvénients
There is so little turnover at SAS, that there is a tendency to get a little parochial in our views, at times. You have to be careful not to succumb to the "Caryland syndrome" where you start to assume that everyone else in the world works in an environment similar to yours...