Yesterday, Google's Head of Webspam, Matt Cutts announced via Twitter that Google had launched an update to their page layout filter:
The link referenced by Matt points to the original post on the Google Webmaster Central Blog back in January this year, introducing their "page layout" filter to the world. The aim of this update was to act upon complaints from search users and webmasters that the quality of results clicked on from a search result was poor due to too many adverts appearing "above the fold", making it difficult to locate the actual page content.
Receptional covered this page layout filter back in January which is certainly worth a quick read to gain a better understanding of what the filter is about and what it does.
Matt suggests that less than 0.7% of English queries will be noticeably affected by the update implemented on Tuesday, so for the vast majority of search users and webmaster it's very much going to be business as usual.
For those webmasters that have seen a reduction in their organic search traffic following this update then a quick review of ad placement is certainly best-advised!