His post on Copyright, Fair Use and YouTube is a classic. On the one hand he says aloud what everyone knows but speaks not: YouTube's entire value proposition comes from breaking copyright law.
One take away is that either the law should be changed, YouTube should reform (come up with a revenue sharing model), or YouTube should go away.
My other take away is to try to memorize the following:
... It's completely glossed over on the YouTube copyright page in favor of 100% original content, but the loophole in copyright is fair use. Under the banner of fair use, you could legally upload a video without the copyright holder's permission. Anyone who contributes anything to the web should have the four factors of fair use committed to memory by now:
1. the purpose of the use [commentary, research, parody vs... theft]
2. the nature of the copyrighted work [esp. whether it's a public good]
3. the relative amount of the portion used
4. the market effect of the use on the copyrighted work