Symfony 2.2 will be released in February 2013 an contains several interesting enhancements, including 2 issues reported or fixed by us.
The way to go would be to switch to dev-master in Composer and do a php composer.phar update symfony/symfony.

Several things to clean up:

• Semantic configuration: Use normalizeKeys( false ) in config tree to avoid key normalization whenever needed (see See https://github.com/symfony/symfony/pull/6367)
• HttpCache: LocationAwareStore should now be based on Symfony\Component\HttpKernel\HttpCache\Store (see https://github.com/symfony/symfony/pull/6016)
• Twig: Default Twig loader is now Twig_Loader_Chain. We can now remove the twig loader filesystem override, and keep twig.loader.string (See https://github.com/symfony/symfony/commit/f48b22a44ea171404471f4371d5f0242705c5f80)