I ended up reading an article over on The Slate today titled A Dog-Eat-Dog World, Does your pet’s food contain dead pets? The article itself was rather poorly written, but the comments are excellent.
I have been aware for some time, at least a decade or so, that commercial dog food runs the gamut from abysmal to excellent. The key thing is to read the label. Avoid foods with generic terms such as protein meal, if it doesn't specify the source then it could be anything. I like The Dog Food Advisor, it has a pretty comprehensive list of the foods available plus they post pet food recalls.
If you don't understand what the ingredients are then odds are you wouldn't want to feed it to your pet.