DuggMob: A WordPress plug-in for Scott
I listened to the CPU Architecture episode today, and was inspired by the suggestion of a universal trackback. Of course, that's a big project, as you said, but scraping Digg comments is relatively easy.
Since I was bored at work, I wrote a WordPress plug-in to do just that. It's in a really primitive state, of course--it's hard-coded to retrieve the comments for your Digg article. The final version will allow you to submit the article to Digg, then hopefully figure out what the Digg story id is on its own and configure itself to show the comments.
The current implementation is
here. Just imagine your content there instead of mine. Or download the plugin
here and take a look at the code.
The Digg API has a few drawbacks. As I mentioned, it's not easy to convert between story name (used in the Digg URL) and story id (required by all API calls). Also, it's read-only, so anyone who wants to add a comment would have to follow a link to the Digg site itself.
Still, I can see people using this, or something like it, in place of (or in addition to) their WordPress comments.
I've been thinking about a universal comment system for a long time, and the trackback idea seems cool. It's worth some more investigation at least.