New service Backtype offers a comment tracking service that doesn't rely on site installs or third party plugins.
The simple to use service starts by asking users for some examples of sites they comment on, then cleverly goes looking for other sites. The process isn't perfect, for example even with my relatively obscure name it still managed to find a comment from another Duncan Riley (there were 14 on the planet the last time I counted) but it is 95% or more accurate, and removing eronous matches is as easy as clicking on a false or spam option.
The obvious parallels are to coComment and Disqus. coComment was the first to offer centralized comment tracking, creating a community around comments. Disqus recently launched a comment blog function where you can share your comments in a dedicated space. Both rely on an install base either on site or in browser, so cannot act independently, where as Backtype needs neither. Backtype feels a little FriendFeed like, complete with the ability to follow people and have comments streamed, and the obvious aside is whether as a standalone idea Backtype works when FriendFeed itself offers support for comments, be it limited in scope compared to Backtype.
Louis Gray is hot on the idea, saying that if you like the idea of a comment blog, you'll like Backtype, which is a fair call, but any of these services ultimately rely on community, and it's far too early to make a call in that direction. There is some social aspects, such as the ability to share, but the ability to connect and comment inline (as is offered by Disqus) is lacking, so there is a stickiness quotient missing. The flip though to that is that the reply option goes straight to the originating site, so it could easily become a traffic driver as well. One to watch.