Various parties have proposed microformats related to citations and distributed conversations. Ryan King and Eran Globen started with hVia (which became citeVia and later citeRel :-)). You can see the conversation in these blog posts:
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.
Citing (quoting as an authoritative source) and hat-tipping (giving credit to a non-primary source for calling attention to a primary [authoritative] source) are certainly two different animals. Common etiquette suggests use of anchor tags because they can be actuated by the user.
I dug around at WC3 and found rel="cite" is already defined in the XHTML 2.0 Hypertext Attribute Collection. Also from that collection, href and cite attributes are defined and may coexist but they behave differently: The href attribute "specifies a URI that is actuated when the element is activated." For the cite attribute, "User Agents MUST provide a means for the user to actuate the link."
Whereas authors in general like their work to be cited with hyperlinks, and whereas users can be counted upon to cite primary and non-primary sources without differentiating, and whereas the only difference between a primary citation and a non-primary citation is the potential for skipped vias, I propose to use rel="cite" in anchors now. (incomplete) - Andy Skelton