I've been reading about all the RIAA subpoenas and it occurred to me that you could introduce a "reasonable doubt" of copyright infringement if your P2P also did *periodic* anonymous proxying. The important point here is that it doesn't necessarily have to be a full-blown proxying system (like FreeNet) with all the performance penalties therein.

Basically, I'm imagining something like this:
- connect to Ultrapeer(s)
- obtain a short list of other nodes
- ping other nodes to see which ones are "close" (in network terms) and to inquire about proxying capability
- establish a co-proxy relationship with 1 or more other nodes
- direct every 10th(?) PUSH request to one of your proxies, along with the requested file

Now, if some enforcement agency comes after you, you can argue -- "I wasn't distributing that file, someone else was and I must have proxied it for them." Since the basic principle of P2P file-sharing seems to be legal, I think this raises some legal doubt about whether or not you are culpable for the detected infringement. Whether or not it's a "reasonable" doubt, however, is another matter.

And -- another after-thought -- if the proxying was done for the more popular files and distributed to unloaded nodes, it could also serve as a performance booster.

If I wanted to achieve security, I would do the following:

In queryhits you advertise your GUID and a 0.0.0.0 IP. In addition you send your push-proxies (your ultrapeers). The downloader sends a download request containing your GUID and the urn of the file he wants to download. The push-proxy then redirects the downloader to one of its leafs (possibly you possibly someone else acting as a proxy) or sends a push to one of its leafs so the download can be started. Unlike your scheme this could work with the download mesh if connections are stable enough.