I began my knowledge management career in 1994, and have managed to learn roughly one new useful thing about KM per year since then.  I hope it's true that "slow but steady wins the race."  Here are my top ten insights.

1. As Thomas Stewart wrote in his book The Wealth of Knowledge, connection, not collection, is the essence of knowledge management.
2. The most useful definition of knowledge for business people is: "the mental capacity for effective performance."
3. The word knowledge is misused often.  If you replace knowledge with experience and the sentence sounds wrong, you're talking about information, not knowledge.
4. If you want to measure knowledge, the best unit of measure is answers.  KM systems are of little value if they cannot provide good answers quickly.
5. It's easier and more effective to manage ignorance, by eliminating it, than to manage knowledge.  Humans' natural ability to notice exceptions and aberrations makes it easier for us to eliminate what we don't want (e.g., smallpox, garbage, air pollution) than to manage, sort, and organize what we do want and have plenty of (e.g., knowledge).
6. Helping people learn what they should be paying attention to is the most overlooked way that KM practitioners can contribute to business success.  Journalists and good bloggers excel at this, and this is one reason why blogging is exploding in popularity.
7. Face to face knowledge sharing is not a luxury.  The pity is that in many organizations it is perceived as being one.  There are indeed examples of effective knowledge sharing in the absence of face to face, but these are far outnumbered by examples of ineffective computer-based and phone-based collaboration.
8. Communities of Passion are what businesses should be trying to create and sustain, not Communities of Practice.  When there is no passion, communities are unlikely to produce useful results.
9. For all the money that many organizations spend on information technology for KM, they often have no more ability to effect change than the leader of a Yahoo! Group has for free.
10. Search is the killer app of document-centric KM, and Google sets the standard.  Social networking is the killer app of people-centric KM, and LinkedIn.com sets the standard here.  Like Yahoo! Groups, both of these tools are free.

Can all this be boiled down into a sentence or two?  Margaret Mead did it decades ago when she wrote: "Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it's the only thing that ever has."