I was scanning WMW and this stopped me in my tracks: http://www.webmasterworld.com/goog/4720495.htm
According to the post citing this resource, "56.1% of all impressions Google measured are not seen, and the most viewable position is above the fold, and not right at the top of the page. "
I pulled a couple comments that I thought were interesting:
From Broadway says,
"Making sure ads remain viewable when using a responsive is difficult. With desktop formats, it's easy to find space above the fold. With mobile, the same high-up ad placement can create a bad user experience because of the lag (blank space) associated with ad load.? ....Adsense should change it's TOS from a limit of "3 units per page" to something like "as many ads as you want, of any size, as long as the total page foot print isn't more than xxx by xxx pixels.""
"...There is a program called MOAT that I know is used by the targeted network and I suspect also by several other agencies that I use. The program does not deliver ads unless more than 50% of the creative is viewable for 1 second. The most disconcerting part of this is that they don't refer the ads to my default but rather they just send blanks that are not counted at all"
TheDonald123 says, "This is scary. My 320x50 mobile ad unit on my responsive site near the top of the page only has a 25% viewability because the ad takes so long to load that the visitor has already started scrolling. Overall very few of my ads come even close to 50% viewability and the lower numbers come mostly from mobile. "
From the looks of this news, I definitely think that this calls for some interesting consideration if you're and advertiser...
See the complete convo in the thread: http://www.webmasterworld.com/goog/4720495.htm