A number of new lens profiles have also been added, along with several bug fixes. Additional release notes are indicated on the respective download pages for each product.
Remember, these are release candidates, which means they’ve been pretty well tested and Adobe thinks they are ready for full release; however, it’s recommended that you keep production work to prior versions until the official releases drop. Expect those to come soon though. Release candidates mean that the final versions are just around the corner.
Lightroom 3.6 release candidate can be downloaded here.
Camera Raw 6.6 release candidate can be downloaded here.