In this recent post to his site Paul Jones suggests that "action injection" in PHP applications should be considered a "code smell" (that is, a bad practice that could indicate that the controller class is doing too much).

Circumstance has conspired to put Action Injection discussions in front of me multiple times in the past few days. Having seen the approach several times before, I have come to think that if Action Injection is the answer, you might be asking the wrong question. I find it to be a code smell, one that indicates the system needs refactoring or reorganizing.

He first covers what "action injection" is and provides an example of how it would fit in with the use of a dependency injection container. He also points to some of the frameworks that currently support this functionality natively. With that defined, he then moves into the main idea of the post - that using functionality like this is a "code smell" that could signal something that is in need of refactoring. He then provides some suggestions on things to change and mental shifts in thinking about how your application is organized. He finishes by pointing to the Action-Domain-Responder pattern as a way of implementing this and how single-action controllers can help.