I have carried both 1911s and Glocks as duty guns, as well as competed heavily with both. I think that for the vast majority of regular handgun users, that RJM is correct. The typical owner does not handle and use his/her chosen style of handgun enough to develop unconscious competence with it. They would be better off choosing one system and sticking with it.
Personally, I sweep the thumb safety (like many here) whether it is there or not. The thumb safety has never been the issue that a grip safety is for me. I tend to have a very high grip/really choke up on a gun and have more than once had to readjust to depress the grip safety properly. If it were not an issue, I would deactivate the grip safety on my 1911s. But it would likely be an issue, so I simply don't.
I have no problem switching between Glocks and 1911s, but due to career paths, I have likely spent a bit more time with them compared to the average recreational shooter.
I would imagine a typical B class or better IPSC shooter who shoots a couple of different classes, such as limited and limited 10, would be in this boat as well.
That being said, I spent the previous 4 years shooting a G19 very heavily. In the beginning they felt awkward and too small. Now, through using them so heavily, they seem completely natural and my G21 seems awkward. Before, the G21 and a standard 1911 were like extensions of my hand.
It is all a matter of training to the point of unconscious competence.
