Google has confirmed that they are rolling out some tests to display different ad placements throughout the search results pages. In this particular instance, Google apparently is trying to display advertisements on the bottom of the SERPs. We're familiar with ads on the right side of the search results, but have you ever seen ads on the bottom?
I suppose not.
However, AdWordsAdvisor confirms that they are running a test on the Australian version of the Google search engine. Screenshots are not available but it'd be nice to see if they settle on it.
Forum discussion continues at WebmasterWorld.
Update by Barry Schwartz: Google has tested displaying AdWords at the bottom of the search results in the past, we have a post from 2005 on that. I have also written a longer post at Search Engine Land on why Google may be testing this out and possibly, why this may become the default.