What about a search engine, where each time you enter a search query (from the same machine), you are served with top results displayed in a different order, and even one 2-nd page or 3-rd page search result (from your previous search) now showing up on the 1-st page?
What is the benefit? It would result in a better optimization of search results displayed to a user, better CTR, and better bandwidth optimization for search engines, and fewer attempts to cheat the search engine via questionable SEO strategies. In short, a win-win both for the search engine and web publishers, and a loss for cheaters.
For those interested in the data mining details, a search engine showing the same results in the same order to the same user, over and over several months in a row (e.g. like Google), is using a basic and inefficient search results scoring algorithm known as "steepest ascent". What I describe here is replacing "steepest ascent" by "simulated annealing" to avoid getting stuck in local optima, and instead, deliver the true global optimum to the user.
: New Startup Idea: A Better Search Engine (part 1)