Do you run Google AdSense Adverts on your websites?
If you do then be careful they don’t overcrowd the page and get in the way of real content. If they do then you may fall foul of a new Google algorithm change that tries to address the fact that most users find these ads quite annoying!
You can read the full article here http://www.seroundtable.com/google-page-layout-penalty-14612.html
and you can have a look at how google may see your website using this tool http://www.browsersize.googlelabs.com/