Big mistake, IMHO. Tags are for taxonomy, not organization. Organization with tags resembles spaghetti. Folders are absolute and cleaner. Anyway, I'm another "I'd go premium, if EN had folders" vote. I'm ready to throw money at you guys if you fix this usability issue.
I understand tags and nested tags, but they suck for my purposes. Great for taxonomy, not great for organization. I would prefer folder and notebook entities. Or notebook and subnotebook entities.