That paper concludes that a substantial proportion of conversions via search-engine ads seem to be sales to loyal users who convert via another channel even when you take away the ads, so the conversion rates themselves may be significant overestimates if what you really want to measure is the net impact of advertising.
The most obvious ones are the "eBay shoes" type of searches, but probably they cost less than "shoes". Still it's a cost. Expect Google, Yahoo and even Bing to fight this tooth and nail, data or no data.
That paper concludes that a substantial proportion of conversions via search-engine ads seem to be sales to loyal users who convert via another channel even when you take away the ads, so the conversion rates themselves may be significant overestimates if what you really want to measure is the net impact of advertising.