Google has stated that bottom ads aren’t a ploy to get advertisers to bid higher to avoid potentially falling into the bottom ads. Like always, ideal ad position depends on the query, the competition and the time. It’s possible that ad traffic and performance, for some queries, may decrease if the ad falls to the bottom. But, for other queries, ad performance may increase. For example, bottom ads may be more noticeable based on how searchers scan the page (eyes directed to the center).
Additionally, searchers aren’t accustomed to bottom ads on Google desktop and may, at first, mistake them for organic listings and more frequently click on them. These factors may increase click-through for bottom ads, especially for query types (like research-based queries) where searchers may completely ignore right-side ads. To increase visibility, right-side ad features like ad extensions are also available for bottom ads.
The point is that ad performance must be continually evaluated and optimized based on balancing visibility and budget, and falling into the bottom ads may be the optimal position in some situations. In other situations, bids may have to be increased to avoid the bottom. In the coming weeks, Performics will pay close attention to abnormalities in CTRs for lower ranking ads.
There is no option to opt out of having ads show on the bottom of the page, and it’s too early to determine how performance can be tracked on specific campaigns. If your selected keywords results in a high volume of paid ads, your ad will most likely not show at the bottom of the page. In addition, if top performing keywords are in the syndicated position, chances are there will be small impact on overall performance.
http://blog.performics.com/search/2011/11/how-will-googles-new-bottom-ads-impact-search.html
