I just read this interesting article on the BBC News website http://www.bbc.co.uk/news/technology-10558258
Over the years, a number of reporters have fallen foul of the rules set by competitions or even Reuters in their attempts to supply what they see as an 'improved' image. It is an interesting (and never-ending) debate.
Post-processing is an important stage in photography, and always has been. The media would have us believe that image manipulation is specific to digital photography, but this is simply not the case.
I believe the purpose of the image is a significant motivational factor affecting the extent to which the image is 'enhanced'. Editors are under pressure to sell newspapers and magazines, so opportunities to alter images will not be ignored.
Many image makers use dodging and burning techniques to give a particular feel to an image, and wedding photographers use an array of filters for the same purpose. Cropping is also used to great effect.
At what point does this become unacceptable?