Digital recorders are essential for good interviews, as are comprehensive notes.
I usually take notes and record interviews. But, after the interview, I often want to go back and find out exactly what someone said at a certain point. In the past I've noted the time (approx. 20 minutes). The LiveScribe recorder has a camera in the tip of the pen/recorder which allows you to point the pen at a note--written in a special LiveScribe notebook--and replay that part of the interview.