It's not only Symfony2, PHP has a lot of high-quality projects going on: Zend Framework, Doctrine, Solar/Aura, Twig, Lithium, Jackalope, FLOW3 and probably much, much more.
Personally I'd be very wary of Lithium as the code looks pretty slipshod internally from a brief scan into it, but Solar and FLOW3 are solid projects.
Didn't dwell too much into Lithium's code but saw they have some interesting ideas also based on 5.3 features, e.g. they use a sort of aspect-oriented programming based on closures and lambdas. Sounds cool, even if only for experimenting with different programming approaches.
It's actually pretty much in the same league as CakePHP: old and slow. Not much to recommend it right now. (Symfony2 actually can pull in Zend-based libraries on its own without a problem, which is why among the more sarcastic of us I've heard Symfony2 described as "Zend 2 but actually here".)
check benchmark: http://www.yiiframework.com/performance/