In fact, the law has never really been applied outside the broadcast and broadband industries, although technically these laws should still apply. The big danger is when someone using your Wi-Fi network leaves their PC on for extended periods and allows other uses to tap into their PC to download files en masse. This is just what happened to a number of unlucky kids who were caught and turned in by their broadband ISP carriers last June, and then required to pay a moderately hefty fine for uploading copyrighted music files. (You can spot a number of them in recent Apple Computer TV advertisements touting the legal iTunes system of music sharing and backed up by the song "I Fought the Law and the Law Won!").
"Any individual computer user who continues to offer music illegally to millions of others will run the very real risk of facing legal action in the form of civil lawsuits," said Cary Sherman, Recording Industry Association of America (RIAA) president, in an official statement released at the time.
The RIAA and other recording industry groups are specifically targeting peer-to-peer networks, like Kazaa, which basically link hundreds and thousands of computers into a mesh network of sorts, allowing users to easily search for songs and other information stored on those computers. Since computers in a Wi-Fi network can easily be linked in ad hoc fashion, multiple systems within your service area could theoretically be engaging in the same activities, but on a smaller scale. The problem becomes much more serious, however, since these systems are most likely connected to the Internet, and therefore can channel requests and data from the Web and into your network.
If you have set up the Wi-Fi system in your building or across your neighborhood (as we many techies have done) then you may be liable for any infractions since you are the keeper of the keys. You may also have some legal responsibility if someone's computer is hacked into and seriously corrupted if you did provide enough due diligence and install adequate security safeguards. Basically, it is a wonderful time to be a cyber-lawyer!