coComment is a site which allows you to track comments you've left across other peoples sites. It's currently in beta, and you need an invite from an existing user to join up.
It sounds like a good idea for those people who don't have a site of their own, but who leave a lot of comments across the globe.
There's a conversation going on at gapingvoid about it now. A quick sidenote about one of the comments:
On a possibly unrelated note-- one of the reasons I never comment in blogs is because there is no threading like in a message board. Perhaps I'm spoiled by LiveJournal but I like being notified when people are responding to my responses.
Why do so many sites have flat comments? Domino based systems have had the ability to support threaded comments forever, I even ran it here for a while (yeah, you can insert a joke about the number of comments I get anywhere you want). It's bred an interesting sublanguage for people who conduct conversations via "bloggenting" (I made that up, I know it's lame) - the whole "@13, you're wrong because you're a n00b" thing which would be completely uneccesary if there was some decent threading/quoting/whatever going on.
It discourages participation from casual users who might happen to glance over comments and pick up on ettiquette they don't understand. It happens in so many places across the Intertron, blog comments and messageboard forums being the two best examples which spring to mind.
Anyhow, if you want to know more about coComment, you can track who's talking about it on Technorati. If you want to know more about making your Domino site support threaded comments, then you used to be able to download one of the notes.net templates and copy the code from there - email me if you can't find it and want some guiding.