In the past two years the ATLAS Collaboration at the LHC has collected a large volume of data and published a number of ground breaking papers. The Grid-based ATLAS distributed computing infrastructure played a crucial role in enabling timely analysis of the data. We will present a study of the performance and usage of the ATLAS Grid as platform for physics analysis and discuss changes that analysis usage patterns underwent in 2011. This includes studies of timing properties of user jobs (wait time, run time, etc) and analysis of data format popularity evolution that significantly affected ATLAS data distribution policies. These studies are based on mining of data archived by the PanDA workload management system.