I don't know what Wordzilla has in mind for the system, but I suppose we could have a list of predefined tags for people to choose from, as generic as possible. You'd have to select from a list that appears after you wrote and submitted your post, you highlight all the tags you like for the post, and after another submittal, the post is up on the forum.
Personally, I like a free system, in where you could input as many tags as you like, but it could end up turning into a hell of a system, with people using different tags for the same concepts, thus creating a folksonomy problem. One upside of this method is that we could have a single field after the "Title" field (when you're writing your reply/starting the thread), and use tag after another using a separator. The first system could also be implemented in the page where you write the post, but it's not as cleaner in my opinion, unless we use a little number of predefined tags.
I wonder if both systems could be used together, using a system like the one the Delicious extension for Firefox employs, suggesting tags based on other tags you already created (in this case, predefined tags in the forum).
I hope all this blabbering makes sense...