1. The 1st organic result gets 30% LESS clicks when ads are displayed above the organic results.

2. Results further down the page get HIGHER clicks in the presence of ads (this surprised us a little).

3. When the Ads appear above the organic results, the organic clicks go down 30%. When the ads appear to the right of the organic results, the organic clicks go down only 20% (for the first few organic results).

I guess this all makes sense. Our eyes tend to scan top and left first. If the desired result is found above the scroll then the visible organic results will take a hit as the ads get clicked. As the searcher scrolls down the page, the ads disappear and the organic results then become the primary target of the click.

What surprises me a little bit is that Google doesn't frame the ads so that only the organic results scroll and the ads remain fixed. This would give the ads a better chance of getting clicked as the searcher begins to scroll down the page...not that I'm suggesting that to happen.

Data from SearchEngineLand.com