I am a recent convert to Zend Framework and I can honestly say that after the first week or so of trudging around to figure out where to put what that I am able to develop much quicker using ZF than I was previously. I have thousands of lines of php code that I wrote for session management, form validation, you name it. In the cases where I decided to reuse that code it has been very easy to extend all the base classes.
The repetitive, mundane tasks, the database handling and queries, the stuff you hate- it's already done for you, you don't have to do it every time all the time any more.
I look at it like this: Even if you or I are personally smarter and better than every single person that is developing the framework, they have more collective talent than we ever can. They are able to formulate ideas, tests, and corner cases that we may never think of- especially on the safety front. I have no experience with Symfony or a lot of other PHP frameworks, but I can say that using ZF in my projects is already saving me a LOT of time.