But regarding pyramid schema, you mean hierarchical structure, right? I have the same concern, but flat tagging does not help much as we can observe from many sites.
Let people browsing from multiple levels of the category is fun. The rule of thumb is: don't expect perfect structure and don't need to have everybody agree on that. Ad hoc hierarchy should be good enough like Amazon product list. Also keep it away from people who don't need to browse it.
I copy-pasted from the site.
BTW, any pyramid scheme is bad and should be prohibited, right?
But the site is cool though.