From the Blender 2.54 development page -
# Big improvements - This software has been used extensively in production of the Durian open movie project "Sintel".
# Feature complete - Although some of the 2.5 targets have been postponed, such as multi-window support showing multiple scenes, a full RNA data level dependency graph, or radial menus.
I also thought some of the rendering engine was yet to be added from the Sintel crew. Maybe I misunderstood?