I had an acquaintance's Hi-Power go FA on me. He had "home-gunsmithed" it a bit for a better trigger. He claims it never went FA on him, but I have my doubts. Anyways, a brief explanation of the consequences convinced him to have it fixed.
Generally, the only handguns that are going to go FA have been tinkered with a little too much. Rarely, a truly worn gun might, or I've heard of it, but have never seen or heard of a first hand account. It is a really, really rare event with a stock gun.
I was shooting one handed when it happened to me, it dumped 8 or 9 rounds, and it was a handful for me. The last rounds went sailing over the berm, thankfully we were on a private ranch and there wasn't anything behind the backstop. It happens so fast that you don't have time to react, all you can do is hold on and try to keep it pointed in a safe direction. I think a worse case scenario would be panicking and dropping it, but I've also heard that the lack of resistance would kill the recoil and it wouldn't cycle if that happened. I, for one, am not willing to try that little hypothesis out.
It also gave me the worst case of hammer bite that I'd ever seen..