graeme_p - 5:14 pm on Jan 22, 2012 (gmt 0)
@deadsea, I also had a 336x280 on the left with content on the right. It was not a site on which visitors had to scroll to see content, except on very small screens (say 400 pixels wide or lower) which suggests that Google is targeting that.
My main loss is of a many first or second places in the SERPs places to Wikipedia and/or a competitor whose ads are lower down the page.
I have replaced it with a skyscraper lower down the page. Now to wait for Google to re-crawl the pages.
This is the first time I am changing a site to suit an algo change, and it does not feel right - when I have lost ground before I have waited a few weeks and my losses have reversed, but in this case it looks needed.