Wojciech Sznapka has an interesting new post to his site today talking about injecting repositories into services in Symfony2-based applications. By injecting just a single repository instead of the entire EntityManager, you get a cleaner, more clear interface defined in the code.
It is generally a good idea to wrap business logic into services. Often, such services methods uses doctrine's repositories to operate on data storage. Injecting whole EntityManager service is very popular approach, but it isn't the most elegant way I could think of. EntityManager works only as a factory in that case and could lead to usage of other repositories, which might end up with too many responsibilities of given service.
He includes some code to illustrate his point - both a "services.xml" configuration of the related dependency injection container and a custom entity repository (defined in the config). He then shows how this repository (FooRepository) would be injected into the service (FooService) via constructor injection.