This change has a number of implications, particularly for those who are executing SQL directly. PDO's API is loosely similar to Creole's, so this change shouldn't require any major re-architecture.

New features that come along with this move you might have to upgrade for include the newer DSN format for build/runtime properties, the removal of the mysqli adapter, SPL autoload integration and a few API changes you'll have to look out for. You can find out more information on the Symfony framework's support for these changes on the sfPropelPlugin and DbFinderPlugin pages.

Using this plugin, it is not necessary anymore to really care about which ORM you pick for your project. It's the thought behind symfony 1.1 taken into the symfony ORM-selection.

He points to the DbFinderPlugin as an alternative to rewriting up the ORM code for your application by hand (or in something like Propel or Doctrine). It makes switching between ORM layers simple - just a configuration change to point to the new system.