I just learned about the idea of graded structure while reading a discussion of the evolution of folksonomies. The idea is as follows:
Of all the adaptations that appeared in information organization [in the 1950s], the most paradigm shifting >may be Ludwig Wittgenstein’s concept of “family resemblance.” With this, Wittgenstein suggested that not >all members of classes are equally representative of the class (Wittgenstein, 1953, in Rosch and Mervis, >1996): for instance, “apple” may be a more prototypical fruit than “tomato.” Rather than assign strict >parameters that all members of a class must meet equally, the family resemblance concept allows for a >graded structure, where members of a class are judged as less or more typical depending on how many >attributes they share with other members of their class.
This concept is a neat one to apply to links on websites. We're accustomed to seeing one single unvisited link color, chosen at the whim of the designer, but how useful would it be to have a browser plugin validate the strength of the correlation between the link text and the content of the page that it links to? Weaker links would be faint, while strongly-related ones would be bold and vibrant (within reason). Or UX designers could take the reins, and design their site to indicate through the visual appearance of internal links the strength of the relationship between your current page and other well-correlated pages that this page links to.
Either way---visualizing the strength of the correlation between link text and page content, or visualizing the relationship between your current page and other pages---links could evolve to show strength through some visual quality (brightness, boldness, color shade, etc).