From Stuart Herbert, a developer on the Gentoo project, there's a post with his perspective on the whole Zend Framework issue, but from a bit different angle than most have come from. He looks more at the Contributor License Agreement.

One thing I don't think has had fair praise has been the Contributor License Agreement. Anyone who wants to commit to the Framework has to sign the Contributor License Agreement first. If you're using someone else's code in your product, it's important to know that all the third-party code is their's to relicense in the first place.

As the FAQ says, if you contribute code to the framework, you're not signing over all rights to your code to Zend. It's still your code; you've just granted Zend a license to use the code in the framework. That's very generous of Zend - they could easily have used their position to gobble up all the rights to all contributions. But I think that it'll also turn out to be the keystone that makes the Zend Framework much more successful than the alternatives.

He also mentions Gentoo's own struggles with this kind of licensing in the past.