From the announcement:
The Blender Foundation and online developer community is proud to present Blender 2.56 Beta. This release is the fourth official beta release of the Blender 2.5 series, representing the culmination of many years of redesign and development work.
This version is called a "Beta" because it's now for the most part feature complete. The Python API has had some extensive changes, most notably in naming conventions and in creation and access of properties.
Since Blender 2.55 beta over 440 bugs were fixed!
IMPORTANT: Between 2.53 and 2.56 an extensive renaming operation has changed the scripting API a lot, with repercussions also for loading 2.53 .blends with animation into 2.56. Make sure you try the FCurve/Driver 2.54 fix entry from the Help menu.