As a mediocre programmer, I probably could have answered the questions at some point in time, but since they are not applicable to my day-to-day life, much of the information has faded away. This has prompted me to refresh my memory, but it is too late for this quiz, as per the requirements.

Assuming you've been in the business for a long time, and not just fresh CS graduate or something, what have you done to stay intimately familiar with the concepts that you do not utilize in any regular capacity?