This document provides a summary and analysis of benchmark data for online advertising performance between Q3 2008 and Q2 2009. It finds that while larger ad sizes tend to perform better for standard banners, size is not a strong predictor of performance for rich media ads, which are better optimized by adding features like video. Overall, the two most common ad sizes are 300x250 and 728x90, comprising 70% of impressions. The document also provides metrics on user engagement for rich media, such as average dwell rates and times.