A post on the Official Google Blog says that the first two search results get most of the clicks:
This pattern suggests that the order in which Google returned the results was successful; most users found what they were looking for among the first two results and they never needed to go further down the page.
I knew you had to be on the first page – but the “top two” result is even harder to achieve.
It is significant though that Google’s post makes no mention of ads. I am quite sure that the study included research into their effectiveness. Google has chosen not to reveal this aspect of the research.
In particular, most Google search results do not look like the examples. Rather, they have ads at the top which look just like the other results, except with a different background colour and a faint “Sponsored Links” at the right:
My question: in a result list like this, which “top two” gets the eyeballs and the clicks? The search results? Or the paid links?