This five minute Freakonomics segment from NPR's Marketplace show should freak out anyone who:

1. Thinks they have a great memory and thus eschew the use of notes, reminders, planners, etc.
2. Is in a position that they are dependent on anyone else's memory in order to stay out of jail or avoid some other catastrophe.

Luckily I have a bad memory and know it so I've developed all kinds of systems to compensate for that fact. Unfortunately my kids also know I have a terrible memory and they use it to their advantage by saying things like, "Dad, don't forget you promised to buy me the new Halo for Xbox today." I've started to wise up and have developed a simple system to deal with that too: if they don't get it from me in writing it doesn't count. 

Here's the Freakonomics segment: