Recent Findings from the Oneupweb study on eyetracking on social networks shows the dominance of sponsored ads:

• 65% of participants engaged with sponsored ads within social networks within the first 10 seconds of their search
• Scan paths do not follow the order of the search. Sponsored ads were looked at before the third or fourth organic results
• There is not a significant difference in fixation duration between Facebook and YouTube

Image below shows eye-track of Facebook indicating the dominance of top results and right hand sponsored ad.

You can download the full report EyeTracking and Social Network report free of charge.