Napster is the most well-known file sharing program. Its a program which was created by a brilliant inidividual who received financing and resources to develop it by open-minded investors and innovators.
The problem with Napster is that it started the debate about intellectual property right laws which are very sketchy and inconclusive. Rightfully, it has been accused of and charged several times and have settled many cases.
However, it started a wave of similar programs, like Morpheus and WinMX which basically copied and improved Napsters program, and which, so far, have avoided major litigation. These companies are here to stay, because of the incredible demand from the public. Once one company goes down there will be two there to replace it.
The restrictions on downloading and searching which Napster has enacted are so severe that it is even hard to find files who are not copyrighted, which has taken the joy out of using Napster for most people. Even though Napster offers a great product, it is barely usable any longer, but one point I want to stress is that Napster did start a revolution on the Internet which will never go away. If you praise them or despise them because of it, that is up to you.