In a context completely unrelated to “threaded” discussion comments on blog posts, Rob Pike once wrote:
Threads are like salt. I like salt, you like salt, we all like salt. But we eat more pasta than salt.
Implementing (what will eventually be) WordPress 2.7′s new threaded comments is not difficult, and doing so yields a moderately useful new organization element: threading, or individual replies, similar to the presentation of discussion forums, many newsreaders, the Gmail message list, or the Twitter @. This post by Ottodestruct has plenty of info to get you started against the latest subversion tip to get threaded comments working in your theme.
I will probably link to a quick alpha Simplish with cut-and-paste test code for a threaded comments template shortly, but I’m interested in opinions right now.