I'm getting so tired of reading Slashdot comments in which the ill-informed hold forth on the fair use exception in copyright law. It is particularly galling when someone makes a pronouncement about a "truth" of fair use that is actually fact-dependent. For example, use of copyrighted materials for teaching has been recognized as falling under the fair use exception. However, that doesn't mean that a professor can just copy a few chapters of this book, a few from that book, and some from another book, slap it together, and use it as a coursebook without paying any licensing fees.
Fair use is a balance that cannot be codified with the sorts of clean boundaries that apply in mathematics. The law is about human behavior, and human behavior gets messy. It gets particularly messy when you're talking about the legal fiction that is copyright law. Pretending that it isn't, and attempting to distill it down to easy pronouncements doesn't help our understanding of it, any more than Lou Dobbs is really telling us what's going on in the money markets. Sure, a clean, crisp pronouncement goes down easy, but it's nothing but sugar water. Unfortunately many people like the taste of sugar water, and they spread the same misinformation to other people. It happens over and over again here on Slashdot, every time a story about copyright pops up.
I know just enough about TCP/IP to be dangerous. So I don't hold forth on the subject. I wish the vocal ill-informed would realize that just because they've read a few comments by other ill-informed Slashdotters doesn't mean that they actually know anything about fair use. Wisdom of the crowds, my ass.