I'd tweeted about my replacement blog engine, and mentioned in my previous post that I hadn't yet implemented commenting. He suggested DISQUS, which is an online commenting service that I'd somehow never heard of. How had I not heard of this?!
From sign-up to comments working and tested, it's taken about half an hour of effort. If you need a public commenting solution, I genuinely can't think why you'd write your own any more. Nice work :)