Do you use them and which one? How it affect your productivity, and how it affects your applications' performance? Is it worth it?
Me personally, I'm all for standardization, but have we gone too far?
Note: subjective rant below - can be skipped:)
I find all this stuff extremely limiting, and I'm not sure even the productivity will always benefit with so much new things to learn (all of a sudden a website "cannot" be built without Smarty, Zend, CakePHP...)
If these are bugless, superoptimized, let me be the first one to embrace them, but I see them as bloated, underperforming tool to create websites with less thinking and more relying on ready-made stuff.
Reusable code - I'm all in.
Standards & efficiency - I'm all in.
But how is a framework needed for this? I have my own templates, classes, scripts, and a standardized way to organize an application that would be very familiar to any other developer.
But, with any chunk of code I (re)use, I have direct contact, I revise it, I want my apps to run as fast as possible and to be optimal in any and every way.
Btw. I also cannot figure these hundreds of people that repeat the "we love wordpress" mantra on their websites, and use wordpress as CMS of choice for both them and their clients.
I really like wordpress, it's great for blogging, or for setting up an affiliate site and getting some SEO love with less effort, but using it to make websites...not my thing.