in our research study, we found the impact/presence of personalization very strong: after about 3'000 search queries, in some cases more than every search query received personalised search results. out of the 10 blue links in some cases we found 6.4 personalised: see for yourself
(search for Hypothesis 1 to get to the data)
http://firstmonday.org/htbin/cgiwrap/bin/ojs/index.php/fm/ar...