If you are one of those who is wondering why your website ranking has gone down suddenly then here is the answer for your question.
Google has launched a new algorithm change where if Google finds excessive ads on above the fold; on your page layout then it can penalize your site or downgrade your website rankings in Search engines.
Google says that user want to see content when they click on a page so website which are giving lots of ads on above the fold space they are going to get affected by the rankings.
Google says that every 1 in 100 searches (1%) have got affected by this new Google algorithm change.
Google has also provided a tool to check if your site is impacted by this algorithm change you can use this tool on http://browsersize.googlelabs.com
So if you are the one who got affected & then make changes in your layout as per the Google algorithm and then resubmit your site to Google.