In his latest post Wojciech Sznapka wonders if Symfony2 is actually MVC or if it's just the "C" and "V" in the equation with the "M" (Model) layer being left wide open.
The question is: where is Model layer in Symfony2? My answer is: there's ain't one and it's good.. Symfony2 isn't hardly bounded with Model layer, as it could have been seen in first version. We can see many Active Record model implementations in modern web frameworks such as Ruby on Rails, Django and symfony 1. I'm not saying those solutions are bad. The main problem was, that big systems maintained by plenty of developers changing over time tends to have a messy codebase. The common place to locate business logic were Model layer. The result of that approach were huge model classes, randomly structured Table/Peer classes full of static method and general feeling that system is hardly impossible to maintain anymore.
He talks about the main problem that comes from this style of coding - overly complex systems - and one possible way to help mitigate them using domain-driven design practices. He lists a few of the things that Symfony2 comes with that could be helpful for this method including the dependency injection container, the use of entities, repositories and value objects.