aristotle - 2:02 pm on Aug 19, 2010 (gmt 0)
I think the effect varies, depending on the search term. The new SERPs page layout that Google introduced a few months ago gives various menu options for refining a search, and these seem to vary according to the search term. Also, for some search terms Google puts up to three paid ads above the organic listings, and these push the number 1 listing down the page and reduce its CTR. But this only happens for some search terms. So the effects of the new layout vary, so that some search terms are affected more than others.