Whenever a method requires a specific data model element type to be set in the call, the type should be enforced.

For instance, calling $entry->setTitle requires that a Zend_Gdata_App_Extension_Title be used. However, if you set a simple string, everything works with the set, but when saveXML or getDOM gets called, it's difficult to determine what failed-- because something like 'Call to a member function getDOM() on a non-object ...*' is thrown.