Pros
1. Office of Intramural Training and Education - They make an effort to prepare fellows for the next step, wherever it may take you. 2. Abundant resources -- resources are available if you are of the disposition to find them. Quite often you may need to circumvent lab politics (starting with your PI) as in anywhere else. 3. The fact that you do not need to apply for additional funding may give you more time to do research and expand your skill-set with other activities available on campus. 4. The opportunity to do "details" (provided your PI allows for it) in other areas of the scientific enterprise (administration, policy, NCATS,...). 5. Numerous opportunities to attend to top notch meetings and conferences. 6. Pay and health care is good (for the postdoc standards in academy).
Cons
1. Completely hit and miss with the laboratory you choose --quite often you do not find out until you are already there. Impressive cover up by senior leadership. 2. Average PI age is +67 years. Quite often: not the most novel ideas. Not the most current in terms of the requirements of the postdoc to join the workforce after this training (what was sound advice during the Vietnam war is no longer valid). 3. Excessive amount of power that the PI exert on the postdocs ("trainees", not employees) -- combined with point 2 4. The "review" process of established researches is a joke (tenure-track is different), which means that not only the "smartest and the brightest" remain. 5. Pay is still low when compared to non-academic positions. 6. Bleak perspectives regarding funding -- flat budget during the last decade...less and less purchasing power for "costly" experiments.