Ok, I'm just finally getting around to testing this out. It's really cool, and in some places can replace auto-playlists I have.
I've skimmed through the thread but if this is in there I've missed it: do these classifications exist outside the hierarchy panel, similar to genre category? I've been messing with location rather than genre. I'm wondering if I have something tagged with, for example, Scotland, which is under United Kingdom, which is in turn under Europe, can I reference United Kingdom or Europe in a search or an auto-playlist and come up with that track?
A couple of maybe bugs I've noticed (or maybe something I'm missing):
I have a playlist consisting of all files from my library and inbox, which comes in at 23059 files, but "All" in the tag hierarchy panel is reported as 22947. This part seems to have sorted itself out. Playlist and tag explorer both report 22946. Maybe something got reset when I deleted that one track.
The filter to show files with tags missing from the hierarchy shows all 22946 files, which doesn't seem right. I have two tags I'm using right now: "location" and "playlist filters". Even if both fields are filled in with correct values, the (!) message will be "No tag hierarchy for:" and nothing after the colon.