Since quite a bit of time, I've been faced with an annoying problem on every projects I use propel on. Propel builders only generates some specific cases selection methods, which consists of pretty ugly copy paste of the same code to populate the objects, and if your needs are not satisfied by the finite little number of propel handled cases, you'll have to either use pure SQL, or write a custom doSelect method. That seems okay at first sight, but it is not. In fact, you're about copypasting the propel generated method, and that's a rude violation of D.R.Y. principle.
I found no solutions during the two last years, but maybe things will change soon with the new sfPropelImpersonatorPlugin. This plugin is aiming at doing arbitrary object population based on informations provided by propel's introspection methods (DatabaseMap/TableMap/ColumnMap) to link populated objects.
The plugin is currently in very early stage, but is working pretty well for my needs, and I'm looking forward to know what others are thinking about it.