This is such a good point. People want the anonymity to trade files but they don't want to pay the performance costs of anonymous networks. The problem is in implementing a trust system based on anonymous peers, when there is no anonymous way to pay for resources.

This is the main reason why I wrote Open Transactions: because providing an untraceable form of cash makes it possible to solve issues of resource allocation on anonymous networks.  If download requests are accompanied by digital postage, college kids will start leaving their computers on all day to collect that postage while anonymous downloads occur through their computing resources. Then when they get home from class, the digital postage that has accrued covers the cost of their own downloads. Effectively, people won't have to contribute cash at all, as long as they are contributing computing resources.

Then anonymous networks can run fast. As a bonus, people can also send each other anonymous digital cash payments on these networks -- and information markets and prediction markets can start popping up.

Bitcoins are difficult to counterfeit because they require "work" aka "computing resources" in order to produce them. SURELY THESE SORTS OF COMPUTING RESOURCES that I have described above, which provide real value to people in the form of fast, anonymous downloads, have some real and measurable monetary value as well? Not only do they require computers to work, but they also provide real value to people on a market where other things are traded.