I found an article about how Google positions their search result and the ads in a way that it is so effective. This feature will for sure attract the advertiser to invest in Google AdWords..
The arrangement made a F-shape area, where user will browse from the left page, vertically, searching for pictures or keywords that they are looking for, and then move to the right side for any additional information.
Reference
http://www.enquiro.com/eye-tracking-pr.asp [Dead link now]