The worst decisions seem to have been using folders, leading to an insupportable number of performance and downstream design problems impacting user experience; and then the decision to make folders of links private by default instead of public. I think tagging is prone to issues similar to folder creation, but the immediate visibility of content on del.ico.us, instead of just the containers, makes the design work better. There's a real immediate payoff without a lot of digging when you look around on del.ico.us.
My links are public, if you want to browse them. See sidebar.