This might be good news for people running adwords campaigns. Less emphasis on jacking up your bid or fucking with the quality score. More focus on writing ads that get clicked!
http://adwords.blogspot.com/2009/08/...h-with-ad.html
We have used a statistical model to account for these effects and found that, on average, there is very little variation in conversion rates by position for the same ad. For example, for pages where 11 ads are shown the conversion rate varies by less than 5% across positions. In other words, an ad that had a 1.0% conversion rate in the best position, would have about a 0.95% conversion rate in the worst position, on average. Ads above the search results have a conversion rate within ±2% of right-hand side positions.