Do porn and other remotely perceived entertainments work because of Mirror Neurons? As you might have known, Mirror Neurons are hypothetically the neuron pair - each of which is carried by other person - that make people to share their feeling although one of them just observes the action instead of take a part in the action. ( This short video is a succinct summary of this neurons, for more see this TED Talk )

the excerpt from the Wikipedia:


  "A mirror neuron is a neuron that fires both when an animal acts and when the animal 
  observes the same action performed by another. Thus, the neuron "mirrors" the behaviour 
  the other, as though the observer were itself acting. Such neurons have been directly 
  observed in primate and other species including birds. In humans, brain activity 
  consistent with that of mirror neurons has been found in the premotor cortex, the 
  supplementary motor area, the primary somatosensory cortex and the inferior parietal
  cortex."


Considering the impulsing effect of Mirror Neurons for the observer, could all these remotely perceived entertainments be taking advantage of these neurons?
I think it is likely the case. I agree that the idea of a "mirror neuron" is a bit dubious, as it implies that the function of those neurons are related to mirroring. It's probably the case that they represent the actual movement, and their activation in witnessing the action is tangential to that. 

As for your question, research was done on this exact topic, with positive results. Mouras et al. found that the magnitude of erection achieved by participants watching erotic videos correlated to the activation of regions known to contain "mirror neurons". 

References
http://www.sciencedirect.com/science/article/pii/S1053811908006897