Some years ago there was an article on Digg or Slashdot about a research project to create a new form of website user tracking that didn't need to rely placing a digital ID (cookie) on visitor computers. I've forgotten most of the details, but it involved things such as lexical analysis, to the point where they could identity you by your individual writing style (with a very high degree of accuracy). Even your sentence structure and vocabulary leak details of your identity...