Obviously, we know that the whole "jumping in the air" part is probably a slight exaggeration on Hollywood's part, but the rest is simple arithmetic: If one gun can kill a lot of enemies, two guns should kill twice as many, right?
Why This Sucks:
Here's a quick challenge: Find us a photo of a police officer, soldier, or any other professional doing this on the job (and not just posing for a photo, either). You won't, because using two guns makes both of them useless.
"Count the number of guns motherfucker ..."
And don't try playing the "it'd be possible if you trained hard enough" card -- the problem is human biology. As you may have noticed, the binocular-like way in which our eyeballs work means we can't see independently with each one, a skill we'd need to aim two guns at the same time at completely different angles, all whilst dodging from cover-to-cover and experiencing massive amounts of recoil that causes the gun sights to bounce all over the place. Enjoy this clip of the certifiably insane hair-beasts over at Mythbusters trying to aim at two targets with two guns and hitting none: