Following a link from Small Pieces I landed at a BurningBird post about a blog threading project:
Project is called Thread the Needle, or “Needley” for short. Its purpose is to track cross-blogging threads.
How it works:
You register your weblog, once, with an online application I’ll provide (i.e. provide your weblog location, name of weblog, email). Frequently throughout the day, the Needle service bot will visit the weblog looking for RDF (an XML meta-language, used for RSS and other applications) embedded within the weblog page. Note that this may change to scan weblogs.com for changed weblogs that are registered, or based on the first time a person clicks the link or some other procedure — testing these out as you read this.
The RDF will be generated by the service now and copied and pasted into the posting; hopefully someday it will be generated automatically by the weblogging tools.
The RDF either starts a weblogging subject thread — starts a new subject – or continues an existing thread. The bot pulls this information in and when someone clicks on a small graphic/link attached to the posting, a page opens showing all related threads and their association with each other.