We've been developing with ZF for almost a year now, and I really have no major qualms with it. Had a bit of a learning curve, but once I understood it, I realized how well put together this framework really is.
Compared to other frameworks, some people might point out the lack of a Model library as being a downside. I actually prefer not being told what to use, and integrating Doctrine with ZF is frictionless. If you're developing in PHP 5.3, and want an ORM, I would highly recommend Doctrine 2 (caveat: it's still in alpha testing).
The other great thing is being able to pick and choose what you want or don't want. I'm not a huge fan of Zend_Form, but I don't have to use it if I don't want to. Also, there's a very loosely structured plugin architecture that lets you really easily hook your own libraries into the framework.
So, I'm a pretty big fan of it.
