Pros
These comments refer only to the theory (PH-TH) division, I have no expreience with other areas. - Large group with experts in many fields. - Enormous number of specialist and non-specialist seminars, often given by world-class scientists - Research only department, no teaching duties as in universities. - Low stress, apart from the pressure you choose to put on yourself. - Very competitive salaries, much higher than most other places in academia. - Generous holidays and many benefits (including great health insurance).
Cons
- Large group, sometimes makes you feel anonymous and isolated. - You have to be very proactive if you want to collaborate with others, people will not come towards you. - Quite disjoint from the buzz of the experiments, you mostly get news through the media, as anyone else. - Sometimes hard to justify your existence!