Symfony 2.0.13 has just been released.
The CHANGELOGhas all the details about the changes and you can even have a look at the fulldiff.
If you are starting a new project, you can get the Symfony Standard Editiondistribution on the download page.
If you already have a project based on the Symfony Standard Edition 2.0.x, youcan easily upgrade to 2.0.12 by getting the newdeps anddeps.lockfiles.
Then, run the vendors script (it also clears your cache):