Via Mike Liksvayer: BlogPulse Conversation Tracker is a specialized search that attempts to build a view of the "conversation" that is created by people commenting on a blog entry around the web.
This is the kind of application that would be so much easier with widespread use of the previously mentioned "Thread Description Language, by explicitly annotating the pages to describe the relationship of the posts and comments to posts.
Instead of having to search, it becomes a simple matter of traversing the links in the documents. A firefox extension that present a three view based on TDL annotation would be great... Unless someone else gets to it first perhaps it's time to spend some time experimenting (please, let someone else get to it first, I'm spreading myself way to thin these days... :) )