That said, I have a few suggestions that could make tagging much more powerful. The first two features on this list were included in the XenTag add-on and were very useful.
1) Allow members to subscribe to tags. They will receive an alert or email whenever a new thread is started with specified tags.
2) Provide admins the option to edit the tag and tag description on the results page for each specific tag. This is especially helpful when the tags are standardized. For instance, the standardized "lord of the rings" tag could be correctly capitalized as "Lord of the Rings" on the tag results page. Editing tag description is helpful for keywords and background on a certain tag.
3) Specific tags (or tag groups) per forum. This is helpful when your site has several different topics.
For instance, I'm in the planning stages of a site for creative people. Let's say I have a forum for painters, and a forum just for musicians. It doesn't make sense to have tags for "acrylic paint" or "paint techniques" in both forums. Also, limiting tags by forum would help ease the clutter by listing only tags relevant to that forum.