While some of your other listed projects are okay (as it happens, Doctrine and Twig are both used as part of Symfony2), Zend is generally considered about as ancient as CakePHP today, and I don't really know anyone who recommends using it for new projects. Most of the "big-name" PHP projects out there are creeping horrors (I'm looking at you, Wordpress), and Zend kinda falls into that bucket.

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.

Strongly disagree. Kohana is, IMO, rather poorly designed (while rewritten, it's still fundamentally all too similar to CodeIgniter for my liking). There is not a strong focus on security[1], there is not a strong focus on modernity--it's inexcusable to not be on PHP 5.3 today, and while Kohana will run there it does not understand PHP 5.3 idioms and features--and the code quality, after auditing, is not all that impressive.

Symfony2, on the other hand, puts a fairly strong emphasis on security, is fully based around PHP 5.3 idioms, and is written with sparkling code.

[1] - http://dev.kohanaframework.org/issues/2766 comes immediately to mind; forget the resolution of the bug (such as it wasn't), the behavior of the developers is not good. I get the feeling from those who've used Kohana that this isn't a unique situation.

Don't know why this was awarded the downvotes. For some types of applications, Kohana is perfectly fine.