An interesting project that I've taken an interest in is BlogMatch. From the site:

If you enjoy reading personal blogs and wish to find more interesting people online through reading their blogs, BlogMatch is the perfect tool for you. Once you joined BlogMatch, it will search for blogs that contain your interests. It also will search for blogs contain unique terms which you are talking about on your blog. It will notify you by email if such matches occur. You can decide whether you wish to read the matched blogs. We hope this service will help you find more personal blogs that better fit your interests.

Although the site is far from done, the 'search' feature went up this past weekend; I had some fun searching for 'tabulas' and finding a lot of returns ;)

The site (I believe) utilizes RSS feeds (full ones) and archives it all so you can match words and phrases.

I wonder how interesting it'd be to add a 'keyword' description to tabulas (add a keyword to your post to define it); you could easily search by keyword or use the keywords to generate a "similiar entries" features. In essence it'd be a cross between categories and autolinks.

Of course, paid users could have an auto-generate keyword feature; a quick algorithm could be developed to parse an entry, lift unique words and see their frequencies. For example, my last entry (would ideally) find the keyword "FOAF."

Even more food for thought.