There's a new universal comment system launching this morning called Disqus (pronounced "discuss") that's aiming to improve the world of commenting for both users AND blog creators. Their take on comments is a little bit like OpenID's stance on logins: give users one identification for many places, while mixing it up with the social tracking capabilities found in coComment and Twitter.
Blog owners who install Disqus to replace their default commenting system get the added benefit of creating a separate forum for each post that mirrors whatever discussion is on the comment thread. In return, users can maintain the same Disqus identity on multiple sites assuming blog owners are willing to buy into the system. Unlike a comment tracking system like coComment (review) however, the onus to be a part of the community falls on the site proprietor instead of the user.
As a commenting system it's very full featured. There's threading that I tested to go six levels deep (a step up from most default comment architecture), and a per-comment voting system that lets users vote on the quality of a response using up and down icons. Users can then sort the comments by chronology, or the most votes on the fly.
Also worth noting is the profile system, which like coComment, lets you see a user's list of comments, and links to where they've been making them. While you can comment anonymously to your heart's content on any Disqus comment board, you can also come back later on to claim your profile in order to start maintaining an identity on other sites--a kind of "try before you buy" approach. If you end up claiming your profile on one site, your "anonymous" identities on other sites will link to your identity.
One neat takeaway is that Disqus lets you track other Disqus users in a similar fashion to Twitter and coComment, throwing all their latest comments (and links to where they've been reading) into one public stream. As an added bonus, each user gets a "clout" rating, which is an aggregate measure of how their comments are being rated in various networks. The higher the clout, the better their perceived reputation is to other casual observers.