Symfony 2.0.16 has just been released.
This version mainly fixes the PEAR packages (again). Twig has been updated to 1.8.3 and Swiftmailer to 4.2.0.
Some changes has also been made in the autoloader. Have a look at the diff or just replace the autoloading code for Swiftmailer with the following line:
If you are starting a new project, you can get the Symfony Standard Edition distribution on the download page.
Then, run the vendors script (it also clears your cache):
$ ./bin/vendors install
Remember that the Symfony2 Components are also available as standalone libraries. You can get them via their dedicated read-only repositories on Github (https://github.com/symfony/Finder for instance) or install them via Composer.