QUOTE(ahoier @ Apr 8 2008, 10:55 AM)

...You think there are some ISPs who simply "dumping" these SpamCop reports to dev/null/ ?...
Undoubtedly there are many. This topic started with the URLs of spamvertized sites. The incentive for the host to crack down on the offending site owner is not huge - although possible listing in the
SURBL and/or an adverse rating in McAfee's SiteAdvisor, etc. might "look bad". But you are talking about
QUOTE(ahoier @ Apr 8 2008, 10:55 AM)

...malware infected systems that are being used to send the large amounts of spam e-mail ...
- which is a different matter, being the sending network and zombie senders. There is some incentive there to act but it is somewhat indirect if the zombie machine follows current "best practice" and sends direct to the internet, rather than through the ISP's mail service. The only thing affecting the ISP then is the cost he can pass on to legitimate users which cost (I guess) is influenced by the volume of illegitimate traffic his system carries and by the bandwidth he can make available to satisfy legitimate users which must certainly be affected by high spam volumes chewing through his recources. If he becomes uncompetitive he loses customers.
He wouldn't/shouldn't care too much about some IP addresses (or range of addresses) in his webspace getting blocked (as such) if they should never be directly sending messages over the internet anyway. You will find these days that most dynamic addresses/ranges are "blocked" on one or more lists anyway - including the one you are interfacing on and including the one I am using. And they will all have "poor" or "indeterminate" reputation scores in the "sender reputation" systems. We don't even have to send spam to be blocked from doing so (by those using the appropriate lists or reputation scores) even before we (heaven forfend) become infected.
Sadly, the internet, in its almost infinite adaptability, can cope with black-hat and gey-hat providers without offering a lot of incentive to the white-hat. Other than the undying gratitude of the few that know the difference between them all.
In some parts of the world providers/carriers have a formal obligation to keep abusers off their networks and to assist innocent/clueless users who get 'borged to clean up their installations. Those providers prime response to date seems to be to filter spam inwards and outwards and to drop the stuff on the floor without notification so that detection and proof of any problem becomes (erm...) problematic. Mind you, the same or very near to it is done by providers elsewhere, those with no such formal obligations, just (deservedly) fragile reputations and beancounters advising them on risk management.
Now I'm feeling all depressed again ...