Everybody is heartily sick of having way too many useless search results delivered. Maybe the page you are after is in there somewhere, but searching within thousands of search results is about as interesting and effective as random browsing.
Today’s invention is to employ the tags which people have used to label their bookmarks as a way to direct search engines to only the stuff which will be of interest to them as individuals.
That would mean that pages found in response to my searches would be filtered according to which best fit the profile of “design(34), brain(30), intelligence(15), robot(15), invention(14)…”
No more need to track the movements of individuals to achieve search personalisation. Just use the tags they have chosen themselves to reflect their interests.