Napster is known as a peer-to-peer service because everyone that participates is supposed to act as a node in a huge distributed storage system. Music is not downloaded from a central computer, it comes via any Napster participant.
Fans of the Napster music-sharing service had better make the most of it while it is still free and functioning.
Some experts are starting to ask if Napster-type services have any long-term future, and if the attitudes they encourage are doing more harm than good.
A study by US researchers has revealed the inequalities of Napster, and the weaknesses of copycat systems that try to avoid legal action by being more loosely organised.
The analysts believe the current band of net song-swappers will be superseded by similar systems set up by the record companies themselves that aim to make money and protect intellectual property.
Napster allows users to search for music stored on other Napster users' computers and then to download a digital copy for free on to their own machines.
The Recording Industry Association of America believes Napster is breaking copyright laws and is suing the service. The case is due back in court this month after a short adjournment.
Grazing lands
Research by internet ecologists Eytan Adar and Bernardo Huberman, at the Xerox Palo Alto Research Center, California, suggests that peer-to-peer systems such as Napster are creating a 21st Century "tragedy of the commons".
The phrase comes from a classic essay by biologist Garrett Hardin printed in the journal Science in 1968.
As long as people only grazed as many animals as the common could support, everyone benefited. However, as soon as people exploited the resources for their own gain, everyone lost out because the grazing land was gradually depleted.
Historians have criticised Hardin's portrayal of events, but many saw a lesson for policy makers, and consumers, in showing the effects of unfettered exploitation.
Now, some are saying that Napster, and many of the copycat services that have sprung up in its wake, encourage the kinds of behaviour that make it harder for musicians and record companies to prosper.
Something for nothing
"The danger is that Napster is training a whole group of consumers to enjoy music without paying for it," said David Philips, chief executive of music website icrunch.
Eytan Adar and Bernardo Huberman believe people take far more from services such as Napster than they give.
Napster is known as a peer-to-peer service because everyone that participates is supposed to act as a node in a huge distributed storage system. Music is not downloaded from a central computer, it comes via any Napster participant.
But Adar and Huberman found that 70% of the members of Gnutella, a Napster-type service, were contributing nothing. The minority is supplying the music for everyone.
"Rampant free riding may eventually render [peer-to-peer networks] useless," said the researchers, "as few individuals will contribute anything that is new and high quality."
The researchers also warn that this unequal contribution makes the services much more open to successful legal action.
Economics of the free
Fans of Gnutella claim it is harder to shut down because there is no central database for lawyers to target. However, the academics point out that because only 30% of people using Gnutella upload music, the service could be shut down quickly if action were taken against this minority.
But there are other, more fundamental threats to the long-term survival of Napster-type services. Philips questions how long Napster has before it runs out of money. "As a business model free cannot last," he said.
Clay Shirky, an analyst at The Accelerator Group and professor of film and media at Hunter College in New York, says Napster-type services may have a limited life because the music industry is starting to catch on and catch up.
Technology tames
"Record companies are realising that making lots of circles of plastic is a really stupid business to be in," he said.
Mr Shirky says the music industry is changing rapidly and recognising that consumers have a need it is not serving.
"Napster has shown that people are willing to break the law to have access to the world's music catalogue," he said. "The industry is looking to licence someone who will play nice with them."
Mr Shirky expects subscription-based systems to emerge that let people download a certain amount of music over a given time period. Music companies are keen on this kind of system because it lowers their distribution costs and improves the return on the artists they manage.
Others are turning to technology to solve the problem of non-payers and pirates.
Systems like Mojo Nation, developed by a company called Evil Geniuses for a Better Tomorrow, try to encourage responsible behaviour by not letting people download everything for free.
Those signing up to the network are rewarded with units of a digital currency, called mojo, depending on how much bandwidth, storage space and processing power they contribute to the system.
The units of mojo are spent when people download anything stored on the system. Mojo can also be bought with real money and used to pay artists who contribute.
Members of Mojo Nation are not anonymous and their reputation for being good or bad citizens affects the rewards they get and who is prepared to deal with them.