Pros
Good cause, many highly committed people, excellent benefits, opportunities for travel (depending upon position), opportunities to learn about local and international labor issues
Cons
As with any organization, whether or not you will have a positive experience depends heavily upon the quirks of your department and its leadership. Failing to make the distinction between those who may have content-area expertise and those with the basic interpersonal skills (let alone leadership abilities) to manage a staff creates highly toxic working environments. While such environments are not present across the organization, they are present and any potential employee would be wise to stay alert to indications that the office they are considering is such an environment.