I just bought a new 3 inch Dynabrade pneaumatic polisher last week, but have only used it once.
It only took me 3 hours to seize my compressor, so it is a must to have a quality compressor (quality meaning commercial grade, not just a big tank). The compressor I had was a good one, but it was old, which is probably why it failed. If you have a basic compressor, it's not even worth picking one of these up.
As far as the machine is concerned, I only have one car under my belt, but it is definitely faster and more powerful than a PC. Under load, the machine runs at 7000 rpm, so it corrects quickly and creates a good amount of heat in a short amount of time. It's definitely not a machine for an ameteur, as it has loads of power and could screw up a finish with one slip.
I will let you know how it goes after Monday when my new compressor arrives!