I have created a testing application with Symfony 2. I noticed that the framework is very complete and powerfull. But there are some holes in the documentation. In the getting started tutorial, there is not any information about the model layer. That would be usefull. More over there is not any full text search engine in the http://symfony.com website. That would be very user friendly.
I have noticed another problem concerning the performances. I have done some tests with Jmeter. Compared with another frameworks, the responce time are too slow. I noticed that compared with Zend Framework, they are 50% longer. Compared with CodeIgniter, they are 650% longer. I think that an improvement is necessary.