coComment

coComment is great, but I was thinking (a couple of months ago, actually) -- why not just implement a simple ping thingy for comments? You post a comment on somebody's weblog/website, you leave a url (perhaps it's your OpenID URL) and the weblog pings you back every time a new comment is posted in that thread. Simple, decentralized and doesn't require any new code to be written other than to put a few existing things together.