I've been reworking the ModelForm class for ZF a bit. Earlier this year, I discussed porting it to use Zend_Db_Table with Matthew Weier O'Phinney, for using it with Zend Framework. I initially had done some checking on Zend_Db_Table, and some small code changes to modify the class to use it instead of Doctrine, but I ran into some issues. Now, I've had some time to think about it, I've reworked the class slightly and added basic Zend_Db_Table support, too...

He talks about the two sides - the issues that came up (including relation support and differences between Zend_Db_Table and Doctrine) and how they were overcome (creating an adapter setup to accommodate for the relations issues).