To answer my own question: http://www.bing.com/community/site_blogs/b/search/archive/2011/02/01/thoughts-on-search-quality.aspx http://www.bing.com/community/si

To answer my own question: http://www.bing.com/community/site_blogs/b/search/archive/2011/02/01/thoughts-on-search-quality.aspx http://www.bing.com/community/site_blogs/b/search/archive/20... Seems it is opt-in users.