To close out our discussion on how to make money with JXTA and P2P, I need to point out that JXTA is not just Open Source and free. If you develop a JXTA application, in many ways you're a part of the community. You're also using the virtual network composed of other peers who are not running your application. So, free software and a free ride on the network. Sounds good—but, as in most communities, it's unkind to take advantage of your neighbors without compensation. In a community, you need to share and contribute as well. You should contribute your time and perhaps some of your code. You should participate in making improvements to JXTA's software as well as to the health of the virtual P2P network. Remember that a community is the sum of its members and diminished by hoarders or non-participants.
Any method you create that makes money should also improve other applications—even your competitors'. Compete on the value of content, the user interface, and by other means. Be wary of competing by creating shadow networks that lock out others. If you hoard, exclude, or penalize parts of the network, you'll quickly be marked as an "undesirable" and perhaps blocked.
You should also avoid acting like Robin Hood—stealing from the "rich" to give to the "poor." The sheriff has a real jail and the court can levy jail time and fines. The rich are powerful and not at all squeamish about making your life hell. Act within the bounds of the law and sound business principles, and your applications will thrive. In the end, only the server industry should feel threatened.
So, pick an application, play nice, and make money. If you are so inclined, by all means, write open and shared software. Either way, change the world by writing P2P applications with JXTA.