By popular request, I've installed a comment preview plugin. I'd tried a live preview, but it didn't display Markdown. Now with a preview and a spell check you can avoid making a mistake in a comment and having Tim Blair write a whole series of posts about your mistake.
I also highly recommend the Bad Behavior plugin to any WordPress users. It blocks 99% of spam without any intervention on your part. Spam Karma 2 then blocks any spam that gets past Bad Behavior.
I'm amazed Blair hasn't offered to back off you if you'll back off him, Tim. I received that offer and I can't be one-tenth as much a burr under his saddle as you are.
Well done!