The Guardian has a brief piece on Joshua Schachter, the creator of Del.icio.us, the social bookmarking site. Schachter is notable for popularizing tagging. Here's a good decriptive quote from the article on tagging:
Clay Shirky, a professor at New York University, studied tagging andadvised Delicious. He describes Schachter as "the first person to figure out the social value of labelling. Any one person's labels are messy, inconsistent and partial, and are therefore much less valuable than formal classification systems. However, if there is a way to aggregate those labels, and therefore their value, they become more valuable than formal systems, because they are robust, socially accurate and cheap."
Schachter recently sold Del.icio.us to Yahoo!. Shirky, who writes extensively on the nature of the Web, is a favorite of mine.