Pros
Dedicated to public service. Because MITRE is not-for profit and has no stockholders, the most effort goes on jobs that are most important to the Government customers. Once you have built up a network of friends among your colleagues, you can find out anything and you canget almost anything done. MITRE is kind to its employees -- not only are the benefits good, but MITRE makes it as easy as possible to get through a personal crisis of health or family. People who have earned trust are actually trusted.
Cons
It can be tough to be a newbie, unless you are lucky in having a first-tier manager who is a good mentor. The various constraints imposed by the Government require patience, Some staff are frustrated because promotion is based on value -- which includes not only technical skill and hard work, but also the ability to have impact (i.e. influence others) and the extent to which your particular skills are in demand.