Some of these may relate to the problems

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Tweaks to handling of anchor text. [launch codename "PC"] This month we turned off a classifier related to anchor text (the visible text appearing in links). Our experimental data suggested that other methods of anchor processing had greater success, so turning off this component made our scoring cleaner and more robust. Improvements to freshness in Video Universal. [launch codename "graphite", project codename "Freshness"] We?ve improved the freshness of video results to better detect stale videos and return fresh content. Fewer undesired synonyms. [project codename "Synonyms"] When you search on Google, we often identify other search terms that might have the same meaning as what you entered in the box (synonyms) and surface results for those terms as well when it might be helpful. This month we tweaked a classifier to prevent unhelpful synonyms from being introduced as content in the results set. Improvements to freshness. [launch codename "Abacus", project codename "Freshness"] We launched an improvement to freshness late last year that was very helpful, but it cost significant machine resources. At the time we decided to roll out the change only for news-related traffic. This month we rolled it out for all queries. More precise detection of old pages. [launch codename "oldn23", project codename ?Freshness"] This change improves detection of stale pages in our index by relying on more relevant signals. As a result, fewer stale pages are shown to users. http://insidesearch.blogspot.com/201...0-changes.html