Sending a thank you note after your interview is a very important step in your job search.

Definitely after the interview. I suggest to my clients, they get some inexpensive thank you cards(3x5), after the interview, go for a coffee, make some notes on what happened in the interview, then write up the thank you with specific points, and offer to further answer any questions they may have. After an hour, drop it off with the receptionist or mail immediately.

Detailed notes during the interview. What is wrong? - poor memory, inattentive, antisocial, lawsuit ....its an interview, not a university lecture. Making a point or 2 on paper, to come back to near the end of the interview I am fine with. Detailed notes, I would really wonder if you are the right candidate.