I don't think it's meant to be strictly hierarchical. Not everything can be pigeonholed. I think the somewhat free-form nature of the wiki is a strength. The category structure is roughly hierarchical, where it makes sense. But I also look at categories more akin to tags. There may not be a single hierarchy that works, there may be multiple orthogonal hierarchies describing articles. See the pages for any of the Mac models…these are categorized in almost excruciating detail to make things easy to find.

This is not to say that there aren't areas needing cleanup, because there are. I guess I'd like to hear more about what you feel is deficient in the current organization. Calling your organization system "arbitrary" at the outset is not winning you points in my book. If you have ideas for better navigational aids, I'm all for that.

[wiki]Special:NewPages[/wiki] and [wiki]Special:RecentChanges[/wiki] are standard features of MediaWiki, and I've been using it long enough that I never thought to link them from the main page, but I just did that since it's a good idea. I'd also like to hear what's broken with wiki tables. They've been working fine AFAIK.