Recently, the archive tags have proved to be very useful as a way to link multiple threads together. For example, this tag search for Ruby shows all of the Ruby game threads, and this tag search for Collective Game shows every thread in the same genre, including Dorf Quest, The Adventuers of Joan and a couple of one-shots.
However, I've had to manually fix some of these tags to help keep them all linked up properly, so it's occurred to me that maybe I need to elaborate on them. If you're adding a thread to the archives, you absolutely should include tags to help people locate them later on. It's especially important if it's part of a series, e.g. the Ruby Quest threads, so that people looking to read all of the content can find them all by the tag.
When tagging a thread, you should include both a specific and a general tag. The Ruby Quest threads are a perfect example; their tags are Ruby, Collective Game, allowing people looking for the specific Ruby threads to find them while letting people looking for threads in the same vein to find more of that type. Don't use ultrageneric, useless terms like epic or tg (are you fucking kidding me?), and try to use terms that others have before you (dorf fortress and dwarf fortress both bring up two completely different sets of threads... and don't get me started on the variations of waaaaagh).
When in doubt, more tags are better than less or none at all, but don't go overboard; the tags Tenacious D, Macross Plus, Spinal Tap, Cyberpunk, Live Aid, Wargames are only ever used once apiece and therefore are little better than no tags at all. They're too specific; a better tag for this thread would have been simply campaign ideas. (Not that this stupid thread should have been archived at all...)
I'm going to write one of those "popular tags" pages that show how many tags are used how many times, which should help users archive threads with useful tags. Again, the ideal tags for a thread contain one specific term and one general term, without going overboard in either direction.
Oh, and one last thing: UBOAAA
Edit: OH YEAH AND PUT A GODDAMN COMMA BETWEEN THE TAGS, GOD