Symfony upgraded version comes with lot of fixes issue. They have added lots of new features but i felt disappointed in terms of performance. The performance has been falls around 30 to 40% in symfony2.1 version.
The following things has been changed:-
The DoctrineBundle is moved from the Symfony repository to the Doctrine repository. Therefore you should change the namespace of this bundle in your AppKernel.php:
Before: new Symfony\Bundle\DoctrineBundle\DoctrineBundle()
After: new Doctrine\Bundle\DoctrineBundle\DoctrineBundle()
Locale management was moved from the Session class to the Request class.
Configuring the default locale