As announced earlier, we are organizing the first code sprint for Symfony 2.3 tomorrow (Friday 12th). If you want to participate and want to prepare your day, have a look at this document where we have listed all current opened pull requests with their current status.
Jean-François also tagged all current opened issues, so it is really easy to have a look at issues for a given component.
Last but not the least, many Symfony core developers will be available the whole day to help you. Let's meet at #symfony-dev on Freenode.