I just finished reading a fantastic article by Lawrence Lessig. If you have ever posted anything to YouTube, or any other place on the web, you should read this article too. I have never posted anything to YouTube. But I have posted videos to my blog and other portals in the past. I have avoided using any music in them for exactly the reasons discussed in the article. I just never have wanted to fight that battle if it ever came down to it. There are thousands, if not hundreds of thousands of others who have borrowed from others to create something new though. Spend 30 minutes on YouTube and you will run across scores of postings that range from downright copyright infringement to completely new works that simply build upon a previous artists.
IMO - This article should be read by everyone and then sent to every government official you can think of. The existing laws need to be updated to modern times. Digital technology has changed the game and will continue to do so. The law needs to adapt and modernize and it should be changed now before it is forced to change by the quantity of material that will be out there. For every one video asked to be taken down from a YouTube, there are countless others that surface on lesser known sites. Eventually a precedent will be set in that there is already so much out that that enforcement will be impossible (it is on the verge of being impossible to enforce now).
The law will change. It should be changed willfully and with thought. That thinking needs to start now.