According to research from DG MediaMind, not all rich media ads are created equal. Those rich media formats that are the largest or most persistent also tended to be most viewable. Overall, 63% of rich media ads served worldwide by the network in September 2012 were considered viewable. Ads like commercial breaks and floating ads with reminders performed significantly above average, with more than nine in 10 placements classified as viewable.
On the other side of the spectrum, enhanced standard banners and polite banners performed worse than the average by this metric. Read the rest at eMarketer.