We have been contacted by a few people last week about a small peak in the number of legitimate emails blacklisted by SORBS, which I believe was caused by escalated listings (see the blog post of SORBS for details). Though we discourage using the escalated zone of SORBS because of the higher chance for false positives (we removed response 127.0.0.6 from the DNSBL definition shipped with ORF a long time ago), some folks still have it enabled.
In short, ISPs do not care much if a paying customers is spamming until the whole IP block gets blacklisted by a DNSBL and other (innocent) customers start to complain. I do not think it’s the ideal way of doing things (i.e. to force the ISPs to get rid of spammers by blacklisting innocent people), on the other hand, I totally understand SORBS and other DNSBLs: they simply have no other choice if the ISP ignores their reports of abuse.
What do you think?