At this week's SMX, Rand made a comment about two big brands that ranked at #2 and #3 for their industry's generic keyword behind an exact match domain. Referring to SERPs Click-Through-Rate data, he suggested that you could calculate how much more traffic the larger brand could receive from the keyword by moving from position 2 to position 1.
At the risk of getting a stern talking to, I'm going to have to ask: really? I'm confident that where you see a well-known brand's site next to an anonymous brand, the recognised name will get a disproportionate number of clicks. The location of each user's click can't be modeled by some exponential decay function; the titles, descriptions and URLs (including the goodwill associated with a strong brand) will have a significant effect on click through rate.