Hmmf. My efforts at updating Elvis Sightings to use third-party comment-threading software have not gone as I hoped. (You may have seen the two test-run posts that I've since deleted!) It took trying out both Disqus and IntenseDebate to realize that any comments using either software would be stored separately from the actual blog -- and there were some other technical issues too. If I were starting a new blog, I'd probably use IntenseDebate. But I'm not starting a new blog.
So, back to our regularly scheduled programming. Maybe one day Blogger will get with the program and integrate comment-threading within their own software!