[behdad]

> How do you measure the question's success? Is there some kind of feedback you get about how the person you made a decision about went on to perform?

Not the latter. However, there are five interviews that each candidate goes through, and as an interviewer you get to read the interview feedback written by the other interviewers as well. So I can compare my assessment of a candidate against four other interviewers' assessment using their questions and feedback notes and rating assigned.