Tags Tag Hierarchy
 

These are just my initial thoughts.

Wonder how useful a a tag hierarchy would be. Where users can give tags a 'weight' when adding them to a thread if they wanted to, enabling us to give other users the option to sort threads by relevance when searching for threads.

Additionally, it would mean those tags that have higher weight appear first in the 'this thread has been tagged with' box. Again giving people more of an idea of what that thread is about.

On top of the it would be permissions based and admin could decided whether to let it be thread based or tag based - the tag based version would give certain tags higher weight always, regardless of where they were posted and by who (this is handy for sites where certain tags have more relevance).