Okay, comment posting is back on again, but with provisos.
All comments are moderated, at least for the time being. So they won't appear instantaneously, only after I approve them. I'll never use this to stop legitimate (human-posted) comments that I disagree with, it's just an anti-spam measure.
However, at some point in the not too distant future, I intend to fiddle around with the templates to permit the posting of registered comments from users of 6A's TypeKey service, which is basically a centralised identity verification service. This will allow you to bypass the moderation stage entirely, and signing up for a free TypeKey identity will allow you to do this across a ton of other MovableType and TypePad blogs and websites too.
I apologise for complicating things, and I hope it won't discourage people who would ordinarily leave a comment from doing so.