Version 2.66 for Blender is still a work in progress, but the development team rolled out a pre-release for the community to help out with testing the new features.
Revision 2.66 of the application introduces preliminary support for hair rendering. This becomes available when the Experimental feature is enabled. Keep in mind that this option is still under development and might disrupt changing of the options along with BLEND files to be rendered differently in future versions of the product.
Also included in this release are UI and usability improvements, which include support for Retina Display, DPI option support for all editors and the availability of transparent tool and property regions.
Mesh Modeling has also been improved as you can now bevel selected vertices. More details about this option can be found on this page.
The full list of changes for this release is available here. However, since this is still a project in progress, modifications are likely to appear. The stable build for this version is expected to emerge around February 15.