Various parties have proposed microformats related to citations and distributed conversations. Ryan King and Eran Globen started with hVia (which became citeVia and later relVia :-)). You can see the conversation in these blog posts:
Here are the basic ideas behind citeRel:
People already cite their sources in their blog posts and it would be great (and shouldn't be too difficult) to track that information. In that vein, read this post which covers the initial thinking on the topic. (This was a followup post).
The basic idea we're trying to solve here is the tracking of distributed conversation- more specifically, distributed conversation between blog posts– the scope is intentially limted here, though other aspects of distributed conversation are certainly important and related.