A nail gun is basically a single cylinder engine, only instead of combustion driving the piston, it's a burst of compressed air, with the exception of some cordless, internal combustion fired nail guns.
Now, as stated earlier, a nail gun can severely injure or kill you if allowed to do so.
I personally know at least 6 guys who have shot themselves or someone else with a nail gun. One gentleman was shot in the crown of his head with a 3 1/4" framing nail. These things can and do happen if you are not diligent with safety precautions.
The main thing is, don't move about while wielding a nail gun with your finger on the trigger. You could easily bump the nose-piece against a body part and discharge a nail.
That being said, a nailgun is nothing more than an innocent bystander and injury cannot be blamed on the gun, it's all operator error.
Here's a link to a quick video of a gun being used to frame the floor of a shed. They are priceless from a production standpoint.:thumbsup:
http://www.youtube.com/watch?v=6fDoWt1fSPc