Just like email, and just like the mobile phone, the 'killer application' here is connectivity and sharing among people. That is the cultural driver of P2P . Most recent attention has focused on the implications of file-sharing for music. And music is a 40 billion dollar business. But recorded music is only one kind of intellectual property.
Words are another - there's an 'open content' movement on the Internet.
Images are IP, too. And you may well have heard about the Free Software movement and the concept of 'Open Source' and open standards. With Linux, thousands of people work on each others' code, continuously - massive testing and peer review that private companies, however huge, cannot afford. Linux is never finished. Its response time to change is incredibly short, thanks to countless people working on it on a daily basis.