Maybe I've developed a compulsion for note taking during my years in college, but I would hate to forget some important or useful info that the interviewer might provide during the interview. I encourage everyone I interview to take out a pen and pad of paper.
Interviews are often information overload.
Combined with nervousness, this can cause major problems, especially for those with short-term memories like myself. If you are unsure about doing so, I am sure that points will not be taken against you if you ask. By all means, always, always take out a pen and some paper during case study questions, unless the interviewer specifies not to. I have a very basic questions. I'm not sure what personal etiquette is, but I would assume that you should unbutton all suit button while seated.