A little word to my fellow bloggers: if you have a new version of WordPress, you'll see how you have a choice between categories and tags. What's the difference?
In short, you plan categories; tags are ad hoc. I would think you would have more tags than categories.
Unitarian Universalist Association would be (here) a category; when I blog about General Assembly, I'll use a tag, perhaps
Here's a good article (pre-tag-functionality) about it: Tags and Categories are not the Same!
Oh, and I have work to do: I have 79 categories, which is far to many to manage.