Posts from both WebmasterWorld and Search Engine Round Table report that Google has been doing some usability testing as of late by experimenting with the location of the top sponsored results.

Basically the test consists of moving the top sponsored results to the side location on a user by user basis. "The rationale is that the user does not want to see the ads anyway and it lessens the chance of a poor prospect clicking on an ad." (from WebmasterWorld)

I think this will have a big effect on the top 5 results because if the top sponsored result is gone there technically should be a better click through rate on the proceeding organic listings. This would also move the 5th Organic listing above the fold making that spot hold greater value.