From a discussion about copyright and YouTube/Google:
The purpose of fair use was to allow use of works when transactions were impractical. In that spirit we should acknowledge that if you use someone’s song in a basement skit that never leaves your basement, that should be fair use. But if 50 million people see the skit on YouTube and it generates $1 million in advertising revenues, that should not be fair use.
In other words, everyone who posts their version of the Numa Numa dance has to get express written permission from the RIAA on the off chance that it will become their 15 megabytes of fame.
Why not just piss on the my birthday cake while you’re at it?