I still use some of my dad's air tools: impact gun, cutoff wheel, air chisel, etc. I do it sparingly because we live in the suburbs and have neighbors close by. It can get pretty noisy. The battery technology is improving so much, air tools are quickly becoming obsolete. Ok, maybe not obsolete, but just not practical for most people.
I am thinking about pulling the trigger on some of the milwaukee battery powered stuff. I have a bit of craftsman 19.2 and my dad has some 18 volt Ryobi stuff. It's more for drilling and woodworking than for mechanical work. I was thinking about one of those impact style tools to help remove stubborn nuts and bolts. I do pretty good with hand tools, but I am starting to get the hang of this "work smarter, not harder" thing.