How far do you want to take this though? Why not just use Blogger or Wordpress.com? Why custom code your own blog?
BTW, I assume you are talking about a custom coded blog (or whatever is being commented) because systems like Wordpress or ExpressionEngine make adding commenting trivially easy.
I have coded my own blog in the past, and yeah, after a while it's boring and so I just use Blogger now. But you can stick comments on more than just blog entries.
At least I was under the impression that you could put Disqus comments on anything really (is that not true?). It would be trivially easy to make a site like HN... just a list of links and with disqus comments for each of them. I am working on a project right now where people can suggest strategies for something and others can comment on them. Disqus would be an easy fit there as well.
You could host your own photos with some quick gallery code too, but why not let Flickr do it? I think Disqus is in the same category.
BTW, I assume you are talking about a custom coded blog (or whatever is being commented) because systems like Wordpress or ExpressionEngine make adding commenting trivially easy.