I used to run a few proxy sites last year and after seeing all the international traffic I decided to take it down. I saw that a few people had went to Islamic militant sites and I was not cool with that. Just last week on my e commerce shop someone attempted to buy stuff using a fake credit cart. My security caught onto them and the card was declined. I looked up that persons IP and saw that it was registered to the planet. I assume that they were probably going through a proxy to goto my site. I quickly reported the activity to the planet and never heard anything back. The moral of my story is this, I assume that if people are doing illegal activities through your proxy, the owner of the domain will be responsible is that correct?
I'm not a lawyer but I wouldn't think so. Gun makers aren't liable if their gun was used in a bank robbery.
I just wrote an interesting post on this subject: http://theproxybusiness.com/2009/01/why-is-tos-important-for-proxy-websites/ Basicaly, as long as you use a proper TOS (Terms of Service) on your proxy, you are not responsible for your visitors action.