What follows assumes you are using Blogger although I assume similar functionality is available with other systems such as WordPress.
You can subscribe to the comments for any Blogger blog using the URL
BLOG_IDshould be replaced by the (wait for it) ID of the blog. So for example, here is a link to the feed of all comments for this blog.
Knowing or finding the ID of the blog you wish to subscribe to is, however, a bit of a pain. If the blog is hosted by blogger (i.e. has a blogspot.com URL) then an easier URL to use is
BLOG_NAMEis replaced by (yes wait for it again) the name of the blog.
A relatively boring post but hopefully it will help at least one person follow the comments on at least one blog!