Just about every blog search engine does a decent job of returning recent posts that contain a particular keyword, sorted by the overall popularity of the blog, freshness, etc.

But what if I want to find a blog most relevant to a particular topic? Every blog search engine does poorly on this task, including the new “blogsearch.google.com”:http://blogsearch.google.com.

Suppose, for instance, that I wanted to find out the best recruiting blogs.

“Technorati’s search results”:http://www.technorati.com/search/recruiting give me fresh postings that happen to mention recruiting, but does nothing to help me find the best blogs about recruiting.

What about Google, the king of relevance? “Google’s results”:http://blogsearch.google.com/blogsearch?hl=en&q=recruiting&btnG=Search+Blogs do in fact include a list of related blogs at the top of the page. It’s the right idea, but their implementation leaves much to be desired. The list is far from complete or authoritative– it has only five blogs of no special relevance.

As I’ve grumbled in the past, the problem is that search engines miss the forest for the trees– they treat a blog as a collection of individual postings rather than as a whole from which a unified theme can be inferred. Fixing this shortcoming is important not only for end user but also advertisers… If you can infer a theme for a blog, you can do a much better job of targeting advertisements that are likely to be of interest to the readers. It’s just too easy to get a false keyword hit on an individual posting and end up with advertisements that detract from the blog content.

No doubt Google intends to improve on the relevance of their related blogs feature over time. I really do think that finding blogs related to a particular topic is a key end user scenario, and that the ability of companies like Technorati to survive depends on beating Google at that game.