... If you do not filter spamers, how do you stop them? If you do filter spamers, how to do stop from occasionally hurting people in Christopher's situation? I dunno. Suggestions?

That depends. If you want to filter abusive senders you have a different problem than if you want to filter abusive traffic. Abusive senders have ways of avoiding your filters; abusive traffic has other ways. Generally a high volume receiver (such as a busy e-commerce web site) has no way to differentiate an attack from a bump in traffic load. Whereas the number of possible sources of abuse ("launch points") is finite. These sources are not necessarily evil but from the reciever's point of view there's not a lot of difference between evil and laziness on the part of a source-owner. In the specific case of e-mail abuse ("spam"), has everybody checked out http://www.rhyolite.com/dcc/ yet? There ARE ways to raise the bar on the sender's pattern selections, at least for e-mail.