I don't have specifics I'm afraid, and it has been a while since I've seen published numbers on this. What I can say is that in most of our categories, if we're not above the fold on page one of the SERP's, we don't get much traffic at all.
Anyone have specific numbers, or a quoteable source from a major site? (If it's not a major site, maybe just give the numbers and a general description of the site, to stay within TOS.)
I think it is possible to get a picture by comparing traffic from listings that recently have changed their position from say 1st to 8th. At least you can see what fraction of 1st position traffic you get from the 8th position.