Most anonymous proxies are designed to support web surfing only. In other words they understand the HTTP protocol but not the special protocols used by the various p2p clients. Even such traditional file transfer protocols as FTP are usually not supported.
Apart from the protocol issue, the main reason for the lack of privacy services for p2p users is
bandwidth. The bandwidth demands in p2p trading are much, much higher than in surfing. If somebody was kind enough to offer a working free proxy service for some popular p2p application, even a T1 line would be on its knees in no time. Public proxies are simply not the way to solve the p2p privacy problem. Proxying itself as a technology can be utilized though as long as the resources come from the p2p community itself.
Freenet uses one kind of proxying to provide privacy to its members but there is a computational cost to it, making Freenet less effective than the mainstream p2p applications.
- tg