Blogboing

you got to read it all

some highlights:

if ads appear above the organic search results and are exceptionally relevant they can get a 10% to 30% clickthrough rate. Ads that appear on the side of the search results are typically much more likely to be clicked on ~ 1% of the time.

the relative click volume of lower ranked results relative to the top ranked site.

Overall Percent of Clicks	Relative Click Volume
42.13%, 2,075,765 clicks 11.90%, 586,100 clicks 8.50%, 418,643 clicks 6.06%, 298,532 clicks 4.92%, 242,169 clicks 4.05%, 199,541 clicks 3.41%, 168,080 clicks 3.01%, 148,489 clicks 2.85%, 140,356 clicks 2.99%, 147,551 clicks	3.5x less 4.9x less 6.9x less 8.5x less 10.4x less 12.3x less 14.0x less 14.8x less 14.1x less
1st page totals: 89.82%, 4,425,226 clicks 2nd page totals: 10.18%, 501,397 clicks

User Intent

Most people who search are looking to research information rather than buying an item, and yet most pay per click ads aim to sell items.

Tip: If a person searches for a research oriented keyword and your listing uses words like compare and reviews in it then the searcher will find your listing more relevant to their needs and be more likely to click on your listing.

Paid Search Ads

If paid search ads appear above the organic search results they drive down the organic search results and take away many of the potential clicks. Google is aggressively focused on keeping attention focused on the upper left corner of the search results, and will only display ads on top of the search results if they have high perceived relevancy driven by a high CTR.

Tip: We typically scan search results in groups of 3 or 4. If 3 paid search ads appear above the search results for a keyword you really need to be in the top 3 organic search results to get much traffic.