Not many people are aware of it, but technically putting music that you don't have the rights to use, on Youtube or some similar site is illegal.
That's right. More than 4/5ths of Youtube is made up of illegal content.
Specifically in Youtube's case, Google and Viacom have been in one of the longest court battles in history. For anyone that doesn't know, Viacom is essentially a big media conglomerate of lots of media companies such as Walt Disney and Time Warner.
A long time ago, Viacom realized that Youtube was pretty much just a haven for young piraters who haven't yet quite discovered P2P. So they did what any American company would do, and took them to court about it.
Since then Youtube has been acquired by Google and such. Some cases were lost, some were won. But really very little was decided. Youtube was still the same as it had ever been with a few changes here and there.
With Google and Viacom's recent court case regarding once again more copyright.
In a U.S. District Court in New York recently ruled that so long as a web entity works together with copyright holders in taking down illegal content when it is found, then they are protected under the DMCA (Digital Millennium Copyright Act)
Basically what this means, is that as long as any website takes down illegal material when it is found. They are still protected by the DMCA. This "website" could be anything. Youtube, Vimeo, MiniNova, isoHunt, Demonoid, etc.
Though this ruling will most likely appealed, for the time being, we should all don a pirate hat and hook and celebrate the good times. AARGGHH!!