Matt Mower writes about Creating Communities From Thin Air:
What I have in mind is a program, I haven’t thought of a name so lets just call it blog connector (BC for short), that you can register your blog with. BC then indexes your blog and creates a list of key words that it thinks are relevant to the content on your site. You are then asked to prune, extend and rank the keywords.
Then BC takes a look through all the other blogs it has indexed looking for blogs whose keywords have similar rankings. It checks to see whether you are already linking to those blogs and if not it sends you a suggestion that you might want to check out that blog and/or link to it. It also applies the same criteria to the other blogs, optionally sending them similar information about your blog.
Matt, we are working on just such a thing with BlogStreet. The first part would be a directory and search engine. The second part of it would work on automatically identifying clusters of blogs (and bloggers). Probably hard to do with keywords only — it will need a mix of looking at the blogroll, links and the text in the blogs.