Starting with symfony 1.1, it is now possible to easily use Propel 1.3 in your project to take advantage of its speed improvements, nested set implementation, object instance pooling, among others. Most importantly, Propel 1.3 uses PDO instead of Creole as the DBAL, offering a significant performance boost.
There's a few steps to getting everything all set up, but they're pretty simple. First, you'll need to grab the right plugin from the Symfony repository, then you change the yml file configuration for the PDO connection, change a few settings in your propel.ini and clear the cache and rebuild the models - you're all set! (Complete commands and example configurations are included)