Trouble is, the coComment website doesn’t use Ajax. Uh, no, wait. It probably does, for the bookmarklet. No, trouble is, it’s not easy for an external website to know every time you comment a blog post, and every time there’s a new comment in the thread. Not easy at all. And the way it’s handled right now is just as inconvenient as it gets: you have to click a bookmarklet every time you’re about to post a comment (which means I can’t post comments from within NetNewsWire, and, more importantly, you’re supposed not to forget to click — apparently there’s got to be a Greasemonkey extension taking care of those matters, but I haven’t used Firefox on my own computer in ages), and then it’ll only work if the blog you’re commenting is using one of six platforms supported by coComment. And, even then, the only replies to your comments that it’ll take into account will be those by other coComment users — that is, the whole point of the system is to have a single page listing all replies to your comments, and it just won’t do that. Do I really have to explain how useless that makes it?
Sure, they’are aware of that, and they have big plans for the future: mostly, they’re going to rely on blog platform developers to integrate some form of coComment pinging or standardized comment feeds in their programmes. Meaning that TypePad blogs and other centralized systems may work soon; WordPress blogs et al. may work someday, but it’ll take years before every install is updated; and some other blogs will never support coComment. And, like I said, if just one blog you occasionally comment on doesn’t support / isn’t supported by coComment, that makes the whole thing far less useful.
Remember the last time someone wanted to centralize commenting systems? Remember TypeKey at all? Sure, Gravatar is doing much better — but that’s because you don’t rely on it: when you post a comment on a blog, you don’t really care whether your gravatar’s gonna be displayed or not. Whereas coComment is more of a productivity tool (yes, even though it’s only blogs), and that means you’ll be pissed off every time it doesn’t work — I’m amazed they don’t even try to guess where comments are in the blog’s HTML pages. That’s the way I’d do it.