Here is a very interesting video about a 6 second drum break that has been sampled hundreds of times and used in many ways, by many creative people, and how this explosion of creative projects that utilized this sample was only made possible because the original copyright owner never pursued any kind of legal action towards those who used this sample. Copyright laws are out of control, and as a musician who uses samples as my main tool, I can tell you from personal experience that it sucks to always have to think about where your sample came from and if it is going to cause you trouble in the future (I don't believe in intellectual property, but it doesn't mean that someone cannot use the government against me in this regard).
Funny as I write this a song by M.I.A. came on and they are a sample heavy band that I hope understands the fallacy of copyright and how it destroys creativity instead of benefiting creative endeavors. Copyright is great for corporations, and terrible for artists.