idolw - 3:16 pm on May 30, 2012 (gmt 0)

>> Also conversion rates are higher the further you are up the page. That's true.

Hal Varian from Google says conversion rates do not vary between positions. There are more conversions at the top, but the rates are more or less the same
Source: [adwords.blogspot.com...]
This is almost 3 years old so take it with a grain of salt.