At the moment, I have a reasonable number of IPs in my filter host list and this seems to significantly reduce the number of spam/bot results. I'm sure that experienced users that visit this forum would have a whole load of bad IPs they could add and if these lists were vouched for by respected users/developers on Gnutella forums, I don't see a problem.

However, I totally agree that in the medium term, banned IP lists will probably cease to be effective as the bad guys introduce dynamic/false IPs - if they haven't already started doing so.