One of the big design choices that Google made when they created Gmail was to drop the idea of folders (or at least user definable folders) and to supply a flexible labeling system instead. My mail filters apply labels to mail from various lists and Gmail makes it easy to view mail with a particular label. If you look at del.icio.us, you’ll see that they came to a similar conclusion as Google. When you add links, you can apply any number of labels to them and easily retrieve links by label later. After using both of these systems, I’m completely sold on the idea that labels should take the place of hierarchical systems for organizing information a lot of the time. I don’t want a file system that is based on labels, but for many other things, labels make sense. One thing that’s worth mentioning is that labels work best alongside a robust search capability.