At the start of the month (October 2012) Google released several updates to it’s algorithm, one of these was called the “Page Layout Filter”. The reason for this update is due to “complaints” Google have received about having to scroll down the page of websites which show lots of adverts to get to the content they are looking for.
Now I am a little sceptical that such complaints actually exist, I think it is more likely Google flexing their muscles and telling people how they want webpages to look like on “their internet”. That aside the update has happened and does make a difference in your ranking.
To be honest moving some of your adverts below the fold and not making the page full of adverts will probably increase visitor enjoyment and might actually increase your CTR!?
So if you have lots of adverts above the fold it’s time to spread them about the page. Another nice little tip, if you have 50 links on a page going external to the site (which is far far too many), make sure you have plenty of internal links on that page too to even it out.