I jot about coComment in early February and had been using it on and off. Aside from the annoying fact that you need to change your commenting habit to make it work (click a bookmarklet before hitting submit), its biggest flaw was not being able to track comments made by non-user of their service. They also require blog engines to modify their code & template to work with their service.
The application idea was great, but that last 2 facts ruined any chance of it really becoming useful. The creator had of course had more than earfull of this feedback, and said to be working on it since early March.
Then co.mments arrived on the scene. It doesn’t require blog engines tweaks, tracks all comments, and even work without you needing an account.

I don’t know if co.mments borrowed the idea as well as the service name idea, but it’s not something someone whipped up on a free weekend. The post crawler is intelligent enough to understand most engines I tried it on. And the no-account mode works well.
Right now, my 2 peeves about co.mments are
- It sometimes get the post title & content wrong. When this happens, it either use the first sentence of a post content as title, or display no titles whatsoever. Having said that, being able to do this much without any change on author’s side is an amazing feat already.
- I have to scroll a lot on the Track page to find new comments. A collapsible interface ala coComment will be very welcomed. (Assaf said he’s working on it.)
P.S. A few days after I started using co.mments, coComment’s host was down for a long period with DDoS attack. Not a good week for the coComment folks.