This involves using Google Blogsearch and in the process I learned a bit about Google search operators. So, my tags are links to a Google blogsearch for the subject word with 'inblogtitle:" Five Wells" ' (it looks like this: bird OR birds inblogtitle:"Five Wells" ). There are some powerful advantages to this system.
1. Search results include articles using the search word whether or not I've included it as a tag. So the tag is really only necessary if the category word is not part of the text of the post. Or as a convenience to readers looking for similar posts.
2. You, the reader, can use it to search for a subject I haven't organized as a category or tag - solving what Coturnix lists as the biggest obstacle to categorizing, namely choosing the categories. Notice Coturnix has twenty categories - entirely reasonable compared to Brad DeLong's sixty-four categories.
3. One interesting way to come up with the categories is to Google your blog for words you think might be important and see how many posts come up in which you've used the word. Caution: use "OR" liberally, for example: bird OR birds.
4. It's a good idea to be sure you link to the search sorted by date rather than by relevance.
5. Reminder to self: until I remember how to force the link to open in a new window, use shift+click link.