Just found out about coComment, a comment-tracking system with a Firefox extension and a bookmarklet for other browsers. It seems to work on both WordPress (including WordPress.com) and Blogger (including Blogger beta) blogs.
Found it through the ecrivains.org blog.
As always, I get very excited at first when I first discover a new tool. This one isn’t necessarily earth-shattering, but it can work very well indeed.
In Firefox, it adds some functionalities to commenting boxes, including a del.icio.us-like tagging system. You can then keep track of posts on which you’ve left comments. Some blogging platforms allow you to receive email notifications when new comments have been posted. But this seems even more useful.