I do, and have seen people running with handguns out of the holsters all the time at matches. I havn't been in a warzone, and don't train by running down tejon street with my gun out.
Don't see a lot of folks around here running around with their guns out other than at matches, but this is just shithole colorado springs. Other places may be different.
I guess I will say this. One poster said something about being programmed to shoot twice, then move. I shoot competitions, but I wouldn't do this. I would attempt to shoot until the threat stopped, I probably wouldn't just stand in place, I'd probably try to make it a little harder for the other person.
If in said gunfight, I had to reload, or was in a bad spot, I'd try to get behind something that would stop a bullet. I don't think however, that I'd shoot, holster, move to cover, unholster and reload, reholster, run to a new place, unholster and shoot, holster.. etc