It was bound to happen sooner or later. Simple lists are great, weighted lists (or tag clouds) are even better. But as data accumulates, its no longer practical to navigate it through tag lists. Some sort of structure is needed. Back in February I had written about tag-sorting, and how easy it should it should be to cluster tags.
Enter categories or clusters as they are referred to on Flickr.
How it works: When you click on a tag, you have the option of exploring different clusters related to the tag. For example, summer has several associated clusters:
