Just a month after the Symfony 2.0 release, it's time for the first bug release. Symfony 2.0.1 contains several minor bug fixes, contributed by more than 35 developers. The CHANGELOG has all the details about the changes and you can even have a look at the full diff.
If you are starting a new project, you can get the Symfony Standard Edition distribution on the download page.
Then, run the vendors script:
$ ./bin/vendors install
And don't forget to clear your cache:
$ php ./app/console cache:clear
You can also have a look at the full diff for the Symfony Standard Edition.