1. The BlogMD initiative is developing a metadata standard for
weblogs and weblogs posts. Join them.
2. As mentioned in the above site, Dave Menendez has developed an RDF
vocabulary for describing threaded discussions, including (but not
restricted to) blogthreads.
3. On the academic side, Simon Buckingham Shum has been interested in
mapping discussions for a few years already. I don't know how easy to
read his papers are, though.
4. Jon Schull has worked on a tool for blogthread visualization and has
discussed the idea of a taxonomy of blogverbs, to describe approbation,
opposition, etc.
5. Wisdom from Dave.