Problogger links to a method at Spide it Grasp it Enjoy it, which is pretty similar to what's going on here, except that the category keywords are inserted manually and then located using an existing site-search engine (technorati, google, or Li Zhao advocates PICO.)
Interesting, but not v. automated, ...& of course I'm going to stick w/ the del.icio.us method, because of the side-benefits of categorising with tags. (posts are cross-listed on del.icio.us, visible in technorati & icerocket tag searches etc...)

Great to see different solutions to the same issue.....