AdWords ads are now displaying in the top 4 and at the bottom, also in a group of 4, in this new Google test. Often, the same ad will appear on the top and the bottom of SERPs - with the same copy, title, and all. The SEM Post reports that it could be a great thing for advertisers, but it also comes with some concerns.
"...it could make things interesting on the reporting end. Does it show as double impressions and how would the cost be calculated, since normally ads at the lower part of the page pay less than the ones at the top, although this can also be influenced b things like Quality Score (meaning sometimes advertisers will pay more for their ads to be displayed when compared to other advertisers on the same page, even if appearing lower within the set of ads.)..."
"...More to the point, will an advertiser pay less if their ad is clicked int he lower set of ads as opposed to the top set of ads?"
Give it a look! Having your ad appear twice on the same SERPs page could be a great asset, but you'll want to know how the cost is calculated of course!