If I were running YouTube, I'd be interested in the suggestion that a fair use argument could be applied as an assumption of promotion rather than infringement. The key passage from that rant:

I believe that such cases occupy far more of a gray area, in which the sharing of other people’s content, in small amounts for no profit, constitutes promotion of the content, and should be considered permissable until such time as the copyright holder objects, at which point it should be immediately removed with complete understanding that both parties acted in good faith.