ken_b - 4:55 pm on Sep 21, 2012 (gmt 0)
In response the the never ending "make ads more visible" guidance from the AdSense team I tried it on about 100 pages.
I replaced a 300x250 ad below the main content with a 160x600 to the left of the main content.
So now the ad and the main content start at the same distance down the page from the top, and the ad block and the content end at about the same point on the page also in most cases.
The result has been about a 50% drop in earnings from those pages.
I'm going to reload the old style pages again.