I would like basic security, this comes in two parts.

First of all, please allow SSL to be configured, even if it's anonymous DH key exchange, that's better than nothing. One of the dorms I lived in had hub style networks, so everyone in the building could see everything you did on the internet, including everything you downloaded with Limewire. :-( It's not a serious issue, but it should be trivial to add a capability to use SSL if both clients support it, considering that the code is already in most JVMs.

Secondly, it would be nice for there to be basic privacy and anonymity. Allow the ultra-peers to have a "host on your behalf" option, where an ultra-peer will pretend to have your files, and will act as an intermediary in all transfers. This could help with caching (perhaps accumulating files on ultra-peers), and allow the edge nodes to remain private. It could also allow an ultra-peer plausible denyability for everything they host.

The best way to do this is to have an "intermediary probability" that can be set between 0.0 and 1.0 by the user. If the setting is at zero, then you never host on behalf of anyone, if it's 1.0, then you host on behalf of anyone. If it's somewhere in between, then you can't really prove that the ultra-peer was responsible for a file because you don't know that he wasn't hosting someone else just because he refused to host you.

That would be a very simple addition that would make the network FAR more resiliant.