On the Zend Developer Zone today there's the first part of a series from Vic Cherubini about an ORM tool he's created to make pulling data from your database of choice (via PDO objects) simpler - DataModler. This first part looks at creating testable models.
DataModeler allows you to create easily testable Models that are not dependent on any datasource. The majority of your logic should take place in the Model, and not the Controller (making your application even easier to test as data sources can be mocked). I try to keep my code as simple as possible, so DataModeler is fairly small.
He talks about how the DataModler tool uses dependency injection and how one primary namespace (DataModlerModel) contains the bulk of the code. He includes code samples showing how to create a simple mode, give the attributes data types and access them via magic "set" and "get" methods. For more information on this ORM tool, check out the latest source on github.