It's a tough subject. The best thing that can be done is implement "display" filters, filters that prevent bad things to appear on your Gnutella client's screen. You'll see more of those now and to come.

The reason this is better than directly filtering network traffic is because of the following: If someone as a developer filters traffic, it gives this developer "control" according to the law; Control over what can or cannot be transmitted over the network. That is one of the (many) things that popular other P2P got into trouble with certain lobby groups (Napster, Kazaa, et al). Once you have such control, it will be much easier that someone requests a developer to filter such-and-such files, be the kind of files you prefer to share/download or not.

Like the Internet, Gnutella is a free and open place, accessible by anyone, anywhere and at anytime, controlled by nobody. Don't let others tell you what you can or cannot access on Gnutella - it's your decission but ALSO your responsibility.

Get one thing straight though: I don't condone illegal activity AT ALL, which includes the kind of activity you mentioned. I'm just explaining the situation from a developers view.