Dealing with so many of these tags myself, I almost have to think that it would be best if only a few--let's say, the moderators--added tags to threads, since the knowledge of similar threads so necessary for effective tag placement is so difficult to acquire in a short time. AISI, tags exist for little other reason than to guide us to other discussions of similar subjects. Most tags, especially the ones that start with a whitespace character because the poster entered tags in a space-delimited list, end up going nowhere.
That's just my personal opinion, though, so take it FWIW.
That's one suggestion, but are the moderators going to want to spend their time categorizing every thread on OC.net? But regardless of who does the tagging, for it to be useful someone would need to go to the trouble of creating a list of preferred terms, standard conventions for names, etc. For example, if you have a thread on Chrysostom, it could be tagged 'Chrysostom', 'John Chrysostom', 'St. Chrysostom', 'St. John Chrysostom', 'Saint Chrysostom', 'Saint John Chrysostom', etc. and the abbreviation St. could be with or without the period and if it's case sensitive (guessing not, but not sure, last I checked and it's been a while SMF ran on Linux which is case sensitive by default) there are a bunch more problems, I'm guessing that using any two of those tags will ensure the pages don't link to each other.
Tagging works best with a list of pre-defined codes, but that's not always practical for open ended topics of discussion.