There are two extremes on the continuum of thought regarding the editing and processing of digital photographs. On one extreme live the photographic purists--those who believe that what you shoot is what you get, and that it is the photographer's responsibility to make sure that the composition and lighting and settings are all just right before the shutter is released.
On the other side are those who believe that Photoshop and its kin were created for the creative, and that enhancing good photos (and sometimes saving otherwise good images from the photographer's negligence to pay attention to that one little setting from yesterday evening's night shoot, and yes I am TOTALLY speaking from experience here) is the right of the artist.
I happen to subscribe to both schools of thought. Sometimes on the same day, even.
I believe that some photos are meant to be enjoyed just the way they were captured. Most nature shots and every photo that is taken to authentically document an event, occasion, or place should remain virtually untouched, save for simple black and white conversions.
Some images are meant to become something more. Textures, color manipulation, and layer blending are my favorite ways to emphasize the mood of a photo. Usually, I am hoping to convey my own emotions about a particular subject onto the image. I'll piddle for hours on just one image until it feels right. Some still life shots, a lot of just-for-fun shots, and even a few portraits can benefit from this treatment.
There is a fine line between thoughtful enhancement and crass misrepresentation of an image. One rule I try to follow is always add--never subtract. In other words, I will add texture or layers or color adjustments, but I will not erase people or elements of the background. Ever. I may opt for a closer crop, but painting or clone-stamping over people or buildings or animals or what-have-you is dishonest in my mind. If I did not want particular people or objects to appear in the photo, I should have taken care of that with the camera in my hand.
One more thing that I would be remiss not to mention: Never alter an image that you did not capture unless you have express permission to do so. Changing someone else's photo--whether it was taken with professional gear, a point-and-shoot, or a phone camera--is bad and wrong. Just don't do it. Not that you would, but I feel better having said that.