The only instance where a Gatling gun(known as a minigun by some of you) is mounted on an armoured vehicle is the 'Vulcan'(means volcano due to the awesome amount of fire spew from it).The Gatling gun is mounted on a M113, this vehicle is used in the Vietnam war by the US. This vehicle is deemed not effective enough when compared to its Soviet counterpart, ZSU 23-4 which is being used by the North Vietnam Army(NVA).It is being equipped with four radar-guided 23mm guns After that there are no more operational examples of Gatling guns mounted on armoured vehicles even for AA roles. The reason is that the Gatling gun is ineffective against armoured targets.
The idea of hand-held miniguns is not possible at all. The minigun which you may have probably seen is in the movie 'Predator' is fake.Weight is a big problem as it is too heavy to be carried by infantry. I mean, you don't see many Arnold-type soldiers in the SAF right? Even if you are able to carry the weapon after a long road march,the recoil from firing the thing will certainly knock you down. Assuming that you can still handle the tough recoil.There will be little accuracy when the mini is to be fired from a hand-held manner as the bullets will be flying all over the place. This weapon fires at such a fast rate that whatever amount of ammo possibily carried by this Arnold gunner will be finish in less than 5 mins of continuous fire.
Maybe it is just me,but I think we have to be more realistic here. Actual war-fighting is very different from what some of you have seen in the 'realistic' movies or computer games. Can't really blame some of you guys as you may not have serve NS yet. I, personally learn the reality of war in the army. For example some of you guys may have associated the scene of an exploding hand grenade to be a great fireball as seen in the movies. Actually this is not true, the typical grenade only contains ball bearings and not some flammable stuff which cause the fireball.What you see will be a plume of smoke followed by a big bang,there is no fireball!

Info on ZSU 23-4: http://www.davidpride.com/Israeli_Armor/IL_Armor_04_307.htm )
Pics on ZSU 23-4:
http://www.globalsecurity.org/military/world/russia/zsu-23-4-pics.htm