MSN has announced that beginning today, you have an extra ad placement opportunity with the addition of a fourth ad in the mainline above the organic results. (Mainline ads are the ads that appear above algorithmic results, and right-rail ads are those that appear to the right of the algorithmic result set.) With this update they are increasing the ads shown from up to 8 per page to up to 9 per page, which means there is an additional ad placement opportunity for advertisers in the adCenter auction. This also means that the top two mainline ads will continue to receive essentially a two-for-one ad placement, since they will also display at the bottom of the page in the U.S. Check out the new addition on Live Search.

Microsoft says they have made this change in response to feedback asking for more clicks for their ads. They say their test results show that displaying a fourth mainline ad, and also displaying the top two mainline ads again at the bottom of the page, increases clicks to these ads. Google and Yahoo offer a max of 3 positions on top, might they change now?