Here is a post from Terry Frazier's weblog: The Power of Knowledge Sharing.  The part about 90% of the corporate knowledge being in people's heads has to be close, even if it's a bit exagerated.

I noticed the grave need for knowledge management and preservation in late 1996.  I worked as an intern at a software company fixing bugs.  A friend of mine from the college also started at the same time.  I had one distinct disadvantage: he was a morning person, and I wasn't.  So he was able to track down our manager and ask all kinds of questions in the morning.  I worked in the afternoon and seldom saw him to pick up all of the great answers.  When I asked any repeat questions, my queries were met with an exasperated expression on the face of someone who was already overworked.  "It's not my fault!", I thought.  "You should write some of this stuff down in a database so I can look there first.  If it's not there, then I will ask you."

So the need became apparent.  There ought to be a way for someone to leave notes about questions answered and problems solved so someone else could search it later.  Imagine that!  I didn't know then that the concept fit into a broader knowledge domain called "knowledge management" (often abbreviated as "KM").