Faceted tagging in the wild

Sara Brumfield and I were talking about tagging as a possible feature in her web-based wardrobe management system Dressr. I suggested she look into faceted tagging a la mefeedia and she pointed out that another fashion site, etsy, already has it. Etsy has one bucket of general tags and a separate bucket specifically for materials. Nice!

Looking around, I see that Emanuele Quintarelli has written about etsy’s other innovative features in the context of faceted classification.

So — how many other web 2.0 apps out there use faceted tagging? By which I mean separate categories of tags for distinct aspects of the items being classified.