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Live accuracy figures for most of the DNSBLs used in SpamAssassin, based on the Oct 2003 mail feed for one user, can be found here: http://taint.org/2003/11/07/184247a_mail.html
Other places to find out about DNS BlackLists / BlockLists:
http://moensted.dk/spam/ http://www.declude.com/junkmail/support/ip4r.htm
Blacklists Compared weekly at http://www.sdsc.edu/~jeff/spam/Blacklists_Compared.html
Current Blacklist Comparison http://www.sdsc.edu/~jeff/spam/cbc.html