I've always figured it's very much a hollywood thing. Come to think of it, it does seem to be in quite a few movies/games; The Matrix, pretty much any Chow Yun-Fat movie, Max Payne video game, etc. I mean, it's possible to pratice a lot and become somewhat adequate with it, but what's the point. I figure it's much better to have one weapon and have control of it. That way the person will actually be able to hit something that's more than a couple of meters away lol. http://www.youtube.com/watch?v=9q4zv2QGdos

One of the reasons it seems to work so well in movies is because the actors don't ever have to worry about reloading or don't care about their gun and can just throw it away when it's empty. So that's another reason why it doesn't work.

As it is pointed out. It's movie style fighting. Real gun battles are never like that in the movies, unless the director stresses on realism, like in Heat or some war movies.

It's like comparing to martial arts combat in movies to real life. There are certain stylized martial arts that were designed to be flashy in the movies to appeal to audiences. Real life sword fights don't last 10 minutes.