Content tagging that really works

Hell Drupalers,

I'm working on a Drupal 5.1 site that will make extensive use of tags, so I need the tagging system to be rock solid. Here's what I've found so far (and what I'm still trying to figure out)

Overview

The site is essentially a group blog. Authors can tag a variety of different type of nodes from a common pool of tags. Authors should be able to encouraged to use existing tags (to discourage duplication), but it should also be easy to create new tags. I also want a simple system of suggesting tags. And, of course, I'd like to use the built-in Free Tagging feature of Categories/Taxonomy so that I can take advantage of the existing tagging modules.

Specifics

Synonyms

I was a bit surprised that the Synonyms field doesn't actually work in Drupal 5.1! I made a simple patch for taxonomy.module so that if a user types in the synonym of a tag, it just links to that root Term for that synonym, which is how I think it should work (before it created an entirely new Term!).

--- orig/taxonomy.module	2007-01-25 16:51:36.000000000 -0500
+++ taxonomy.module	2007-05-09 15:15:12.140625000 -0400
@@ -816,6 +816,12 @@
         // See if the term exists in the chosen vocabulary
         // and return the tid; otherwise, add a new record.
         $possibilities = taxonomy_get_term_by_name($typed_term);
+        
+        //----Added by ESD - 2007-5-9 - Check for synonyms before creating a new term. 
+        $syn_root = taxonomy_get_synonym_root($typed_term);
+        if($syn_root) $possibilities[] = $syn_root;
+        //----
+        
         $typed_term_tid = NULL; // tid match, if any.
         foreach ($possibilities as $possibility) {
           if ($possibility->vid == $vid) {

Suggesting Tags

I've created a simple module that adds a "Suggest Tags" button under every "Tag" input field. It passes the contents of Title and Body fields through the Yahoo Term Extractor (yahoo_terms) and then weights the results based on what keywords have previously been used as tags (the idea here is that tags that have been used more frequently in the past are more likely to be good, but YMMV). I'll post what I have if there's enough interest, but it's a work in progress.

Tag Admin screen

I want an easy, one-click way to say that tag A is a synonym of tag B. It should retag all content tagged "B" with "A," delete tag A, and list A as a synonym of B. Anything like this already out there?

Initial Tag List/Tagging Old Content

I've got a ton of old, untagged content that I'm importing from Drupal 4.6. The plan is to run the Yahoo Term Extractor over all the content and then drop everything except the Top 100 tags (and merge the ones that are synonyms, delete the meaningless ones, etc by hand). A quick proof-of-concept test shows that this works alright. Any other ideas?

Finding "Related Items"

I'd like to have a feature that suggests related nodes. I'm guessing the algorithm will be something like: search for other nodes that have the same tags, and then order by number of matching tags and then by date. (kinda like this snippets). Maybe there's some way to incorporate data from the Search module too?