I played with the Movable Type Tags plugin tonight. It was...almost a great thing. I can see where it would work well for a lot of things, but ultimately, I uninstalled it.
The tag concept is actually very simple: it replaces “keywords” with a field called “tags.” Then, whenever you save an entry it parses the tags and does one of two things:
If it finds a category named the same as the tag, it assigns the entry to the category
If it doesn’t find a matching category, it creates it, then assigns the entry to it
This means you get a category for every single keyword you’ve ever used. And if you have category archiving turned on (most people do), you get an archive page for every single keyword.
This may be just what you want...or it might not. The thing I didn’t like is that it seems to be hard-coded into splitting the keywords field on spaces, not commas. When I put these keywords in an entry:
Bill Gates, Live 8
I ended up with four new categories: “Bill,” “Gates,” “Live,” and “8”. Not quite what I intended. I think I’d need to put underscores in the text or something.
So, the bottom line is that this is an all-or-nothing type situation: either you have categories, or you have tags, but they aren’t really going to co-exist very well.
Again, if you have a new blog, and you want to do tags from the start, then you’re set. However, if you have hundreds (thousands) of entries that have been “keyworded” without the intention of using those keywords as de-facto categories, then you might have your work cut out for you.