I've installed phpbb at http://theclapp.org/fora, and created three fora, one for comments on blog entries, one for comments on lw-vim-mode, and one for other stuff.
I didn't really like the idea of using the wiki for comments. In my experience, comments in wikis are poorly attributed and the threading sucks. Perhaps ironically, I've installed phpbb, which doesn't do threading, but at least you can quote people more easily, it's a little more obvious who wrote what, and it's generally a nicer interface for a conversation than a wiki.
For now I left it as a public interface: you don't have to register to comment. If that doesn't work out then I'll change it.
On the other hand, I've no good idea who all reads this, so I may just be shouting
in the wind. 
On the gripping hand, I know that Zach reads it,
so that's one. Hi, Zach!
Update 14 Apr 2008: I got spam and no comments, so I deleted two fora, which still allows comments but makes it easier to delete spam.
Update 22 Apr 2008: I really don't blog enough to have a lively comment area, more's the pity, so I disabled the fora. If and when I blog enough or get enough commentary in email, I'll reenable it. Frankly I doubt that will be any time soon. Ah well.