Chris Shiflett has some good news for all of the Zend Framework fans out there - the license that it's under is now compatible with the GPL.
This means you can use the ZF for your own GPL-licensed PHP project. The big change is the removal of the advertising clause: 'Redistributions of any form whatsoever must retain the following acknowledgment: "This product includes the Zend Framework, freely available at http://www.zend.com/"'
Chris notes also that it's a welcome change over to this pre-existing license to reduce the number of licenses that companies would have to change/evaluate.