This may have nothing to do with personalization. http://googleblog.blogspot.com/2008/09/search-evaluation-at-google.html http://googleblog.blogspot.com/2008/09

This may have nothing to do with personalization. http://googleblog.blogspot.com/2008/09/search-evaluation-at-google.html http://googleblog.blogspot.com/2008/09/search-evaluation-at-... "We also make use of experiments, in which small fractions of queries are shown results from alternative search approaches." Many small experiments can lead to differences for a reasonably large fraction of queries.