My apologies to anyone who may have commented in the past, but had the comment disappear down the plug-hole.
I was using the Akismet plugin to capture comment spam, and seeing as none got through I figured it was working just fine. But then I started to look closely at the stats, and things didn’t seem to add up. I therefore suspect that the filter may have been marking some comments as spam when they weren’t. I have therefore temporarily disabled that plugin. Let’s see how it goes for a little while.