ZF2 may fix a lot of the complaints I (and other folks) have with Zend, but right now it's really hard to recommend it.
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".)
Well, Symfony2 itself only until very recently was using some of the ZendFramework libraries internally (and Fabien often praised ZF), which I would say comes as a proof that it is a solid code, even if it's obviously lacking in some parts comparing to younger alternatives. In many cases it's still the best thing in the market though (Zend_Search_Lucene, Zend_Pdf, Zend_Amf, Zend_Gdata come to mind).
Well-written code can still be old and slow. ;)
A big shout out to Yii Framework - its really fast!
check benchmark: http://www.yiiframework.com/performance/
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.