It was quite common to use Zend_Db_Table as base models class, but it was simply not practical. When you start dealing with relations and hierarchical data types it starts to get really tricky, because simply Zend_Db_Table doesn't provide an extensive enough functionality. So half a year ago Zend Framework developers started to look for better solutions.
An alternative (and a very powerful one at that) was found in Doctrine - an object relational mapper tool that sits on a database layer. Doctrine 2 will even be the first ORM with seamless integration between the Zend Framework (and Symfony). He briefly touches on what some sample code might look like and the command to build out your model classes from predefined YAML files.