A common feature of these complaints is that the person making them will often threaten to sue if the listing isn't removed. This is funny on several levels, as well as usually being quite naive legally (the common wisdom on the anti-spam side is that SPEWS is doing nothing but publishing opinions about who is a spam supporter, period, an activity protected by the First Amendment).
Today, a sysadmin for the American Bar Association posted, saying that their systems were part of a SPEWS listing. The posting was refreshingly clueful, and notable because they did not make any legal threats at all. Perhaps the ABA is more professional than a bunch of spammers, after all...