Created by Matthew Evans in 2002, the goal of the blackholes.us site was "to create (yet more) DNS blocklists of spammers, spam supporting ISPs, spamware hosts, dialup networks, and other notorious email abusers originating in the United States." Matthew published many different DNSBL zones, listing various countries, ISPs, netblocks, etc.
It is now no more. As of October 11, 2009, the website at www.blackholes.us makes it very clear that the blocking lists are no more, and should no longer be used: "The listing services that used to be part of BLACKHOLES.US is no longer alive. The IP address space that they used for name servers now belongs to another, unrelated entity. We would like to use our space without the tens of thousands of DNS queries per second coming to us. So it would be MOST USEFUL if you or your email administrator would REMOVE any reference to blackholes.us from your anti-spam system. There is no LIST REMOVAL service. The "removal" process is simple, DO NOT USE the BLACKHOLES.US domain for your filtering or anti-spam system."
As reported today on the SPAM-L mailing list, all queries against the blackholes.us zones result in a positive match -- meaning that if you use this DNSBL, you will block 100% of your inbound mail attempts until you remove any reference to blackholes.us from your mail server configuration.