I think this is one of the most underestimated or ignored spells in the whole magic-section. Regarding the description, the spell gives you bonus-dice for operating any device the spell is cast on. But how far does this go? If i cast this spell on a commlink, does it mean that i am capable of hacking, electronik warfare and everything else that would be possible with this gadget, and if i cast it on a firearm, does it help to shoot? My comrades argue that the spell just gives you a clue how to dissemble/assemble the gun, attach upgrades etc. but if the spell would be that limited, it wouldn´t be worth the karma to learn it. Because you can only use bonus dice above the OR-frontier, it is limited enough in my point of view. So i´d like to get your experiences. Do you use this spell and if you do so, how?

Well, considering that Object Resistance is now 1 (Natural), 2 (simple manufactured goods, like plastic, brick, leather), 4 (most firearms and electronic equipment), and 6+ (all commlinks and computers, drones, and vehicles), you'd be hard-pressed to get enough net hits to beat those thresholds on most useful tasks. Not to mention that you're going to be sustaining the spell (if you aren't, then you are using a sustaining focus or quickening, both of which are fairly obvious on the Astral Plane), further reducing the utility.

Still, I recognize your fellow gamers' concerns. It could potentially be abusive, depending on how strict or lax your GM is about Object Resistance thresholds, summoning spirits for bonus dice, and drain rolls.

By Rules As Written (RAW), SR4A p206 states:
"This spell allows the subject to analyze the purpose and operation of a device or piece of equipment within range of the sense. The caster must gain enough hits on the Spellcasting Test to beat the item’s Object Resistance (p 183). Each net hit gives the subject a bonus die while operating the device, and allows the subject to ignore any skill defaulting modifiers for using the device while the spell is sustained."

In my game, I would treat it as a perfect technical understanding of the device and its intended application. You know every feature, the entire owner's manual and the things the engineers left in for troubleshooting and never told the end-user about. You also know the peculiarities of this particular device - the loose power coupling, the memory overflow that causes it to hiccup whenever it tries to play video and respond to wireless queries at the same time, the way the balance is slightly off...you know the device like someone who has been using it for thirty years.

I would allow this to give dice to the Computers group, since you would still need to invest in the equipment and programs to actually use it, and you'd still only get a fraction of the dice the team's technical expert will have.

The degree to which this helps with a skill should have a lot to do with how much of the work is knowing how to use the device. A lock, for instance, should be easy to open once it's inner workings are understood - poke it *here*, shoot it *there*, or run current through *this* screw for five seconds. A gun is a combination of knowing the weapon and being able to use your hands, arms, and eyes to put the weapon where it needs to be - I'd rule that it could give you the equivalent of a Specialization in that weapon (+2). To extend the example further, consider a sword. Knowing what part cuts doesn't help you get it into the bad guy; the user has to do the work himself.

@hahnsoo: the errataed ORs of SR4A only go up to 5+ but this is still a lot.

@MikeKozar: The description is pretty unambiguous. If you get enough hits you get bonus dice, operating a gun includes shooting it as does swinging a sword. According to the description this bonus is unlimited, but, besides having to roll that many hits, you need a force equal to OR+hits to actually use them.
To me this is not unbalancing. Especially since you need two additional hits to overcome the sustaining penalty unless you use a focus or quickening. This penalty persists for all actions not involving the device.

This is the same problem as with the sprites' power Diagnostics. From the name you do not deduce that this actually helps using the device but the description says otherwise.