Technorati has come up with another good service called Blog Finder that can let you search for blogs as per categories or subjects, as tagged by the blog-owners. IMHO the tagging part should have been a moderated affair, current system will have all the drawbacks of tagging. This could do well for blogs that do not have categories, like the Blogger blogs. As of now Technorati (and I know this using their BlogPostTag API) used to regard the categories in blog systems such as WordPress as default tags. Now I am not influenced by the bashing Technorati has been getting lately, but frankly, I would still prefer Google to search for blogs on a subject. [Source]