According to my referrals, the 2nd and 3rd page is less than that personally.
To me the first page is important, and getting above the fold within the top few positions is where the true bang for your 'buck' is at. There is a big difference in number of referrals for popular keywords between 2 and 9. 10 can be good, and 11 can be better than 9 even I think some times.
My goal - first page, above the fold.
Here is an old copy of an eye tracking map. The colors show more eye movement in the red, etc areas and continues to be considerably less below the fold. If you look at the top center of the graphic, there is a tiny white bar graph with the color chart percentages. Red= 100%, Green=50%, Blue = less.
On the flipside of all that, I also tend to think that some of the visitors who do find you on the second or third page can be more qualified (i.e. convert better) - the reason being ... they are more serious and farther along in their buying process + comparing your site to the previous ones they have already viewed on the first page. I'm not saying anyone will sell more being on the second page, but I do tend to think the audience you get from those visitors is a bit different from those typical to the first few results (people browsing).