Search engines aim to keep the search index clean – after all, if the results are worthless, few will continue to re-use their service which means lower profits through search ads.
Mid this year, a German SEO reports on Google’s Secret Evaluation Lab at eval.google.com. On the Yahoo front, Search Engine Watch also revealed that Yahoo was recruiting Relevance Analysts. Now MSN appears to be joining the hand-editing wagon as well.
Not really a surprise that humans do a far better job at filtering results than algorithms can at the moment. This probably won’t change anytime soon because algorithms are designed by people and people can always find ways to outsmart it.