I spotted an interesting commentary on the lifecycle of a blog discussion over Simon Phipp's blog. I think its one good way to look at it. I do think there are some things that could be done to make conversing about a blog topic easier on the actual blog itself. The fact that I don't ever get notified VIA mail or RSS if someone responds to a comment I leave on their blog makes the blog comments a lot less useful than they could be for on topic conversations. I think because of that this lifecycle is a bit more forced upon us than it should be.
On our internal blogs at Sun, I stumbled across a good reflection by a colleague (and related comments by others) on a weblog I'd not previously encountered (I'd spotted comments like those made by James Tauber, but only because of Technorati, I had to work at it). The problem with trying to have a discussion spread across a myriad blogs is there's no meaningful way to read it.
I would never have read the comment (about wanting to use trackbacks and blog-hosted discussion) if I hadn't just stumbled across it, and if a newcomer to our conversation wanted to see what had come before s/he would stand no chance of finding all the blogs involved and threading together the comments in an order that made them intelligible. The discovery seemed to me to demonstrate the problem with a blog-centric approach to conversation (something that's bugged me for ages)....Both trackbacks and blog-hosted comments fragment the conversation and keep blogs an echo-chamber rather than part of a discussion flow with a conclusion. In a peer community, I believe discussion forums (of some sort) need to be the centre of the discussion, with blogs and wikis at either end end of the flow.