I bumped into coComment finally. It's an interesting idea, almost identical in its end results to SXORE (which should be more officially launching this week, I think). But, the way it works and why you might want to use it is highly different.
coComment gives you a little "bookmarklet" to drag to your toolbar, and you click it whenever you see a comment box you want to leave a comment in. It sends your comment back to the central coComment server and you can of course track things via RSS and all that good stuff. The comment still lives in the original spot on the original blog...it just happens to be tracked centrally as well.
How is this different than SXORE? Well, at it's core, SXORE is based on identity, and could replace/augment the user login process of many types of systems. coComment is more of an overlay system, however at the end of the day it is tied to your coComment username, which is also an identity of sorts. What would be really interesting is if coComment actually begins SXIP-enabled -- that your coComment username is one of your identities, with which you could login to all sorts of things.
I suspect that usage of coComment will grow *much* more quickly (it only requires a browser an account to work, and no modifications to many existing blog systems), but what it enables is much less interesting than the eventual promise of SXORE and other identity systems.
You can find my test comments at http://www.cocomment.com/comments/boris -- in my short testing, it doesn't work with Drupal or Roller (two posts I just happened to have open), and it does work with WordPress and TypePad.