Well, seems that JDarcy sent in a comment, but changed the subject line so the comment processor rejected it. I thought the subject lines were odd enough looking that people would realise they denote the entry to be commented (or the comment to be commented in the case of threading).
Anyway. The processor (silently) drops malformed mails so we will never know what insightful words JDarcy had the world (unless he reposts).
Having said that, noone has yet managed to get a comment up. People have even mailed me about the comment system rather than post a comment!