Right, time for a lecture!
There seems to be a lot of opinions on here but not much theory or fact. An induction kit works on one simple principal - to improve air flow to the engine. Any high performance air filter will do this. The problem is however (and the reason there are people on here saying they do nothing) is that a lot of induction kits suck in warm air from the engine bay, negating any benefits of the increased flow. You see, warm air is less dense than cold air i.e. for a given volume of warm air, it will contain less oxygen than for the same volume of cold air. Critically, fuel needs oxygen to burn (remember your fire triangle from school!!) and therefore the more oxygen you can supply, the more fuel you can burn and hence the more power you can make.
Modern induction systems are very restrictive due to NVH requirements. They are specially tuned to cancel out induction noise and as a consequence become convoluted and inefficient.
What is required, therefore, is a high flow filter that has a cold air feed. That is exactly what Pipercross are trying to do with their V-Force (and they are not the only ones). You cannot judge this on previous experience of, say, K&N 57i kits or whatever. The V-Force will provide a cold supply of air and a high flow filter and I have no doubt that it will improve power. Having said that, they seem to be using a lot of elaborate and largely unnecessary materials in it's construction which is putting the price up. I have made many home made induction kits from old air boxes, Samco hoses and universal cone filters with very good results.
If you are getting more oxygen into the system, you will need more fuel. Nearly all modern engine management systems monitor the air-to-fuel ratio and will add more fuel to maintain an optimum A/F ratio (of around 14:1, I think), within pre-determined limits.
As a slight digression, another way of gaining power from induction kits is from using ram air effects, but you need a very direct induction routing to achieve this and I don't believe the V-Force will provide this.
With any tuning it is important to understand what is trying to be achieved. There are so many myths surrounding horsepower. Horsepower is calculated from torque. It is very important to know this. Torque is what governs acceleration, not power. This may be tricky to get your head around, but go with it. When you accelerate in any given gear, the peak acceleration in that gear will occur at peak torque, not peak power. If acceleration was governed by power, the rate of acceleration would keep increasing as you go up the power curve, and this doesn't happen. As the revs go up, you obviously continue to build speed, but the rate at which the speed is building is directly related to the shape of the torque curve. If you have a flat torque curve you have a constant rate of acceleration. If you've driven a modern turbodiesel you'll know that you get a big dollop of torque followed by not much. To relate this to the torque curve, the torque curve rises steeply for about 2500rpm and then drops rapidly. My point here is that you should think of power as the engines ability to sustain torque as the revs increase. And power is equal to torque multiplied by engine speed.
Now, this relates to induction kits because when you fit an induction kit, you improve flow and therefore the breathing of the engine, throughout the rev range but particularly under full throttle and at the top end of it's rev range. Even if the peak power figure is hardly improved, the engines torque curve will stay flatter for longer. For example, if peak power was 180bhp @ 7000rpm with the standard induction system and 183bhp @ 7300rpm with an induction kit, the engine is maintaining a higher level of torque for an extra 300rpm. So, when you're accelerating flat out (at Santa Pod or wherever) using all of the revs, the engine will sustain the pull on each gear for an extra 300rpm. It doesn't sound like much but can be worth a couple of tenths of a second over a quarter of a mile. Also, if (and this is a big if) the torque is improved throughout the rev range, then the car will accelerate more quickly in each gear.
In general, induction kits don't often offer a noticeable increase in torque lower down in the rev range, hence when fitted they don't provide an easily noticeable change in performance and hence why people on here are saying they do nothing. Plus, in normal driving when you are not using all the revs or full throttle, there is little or no difference in performance.
So, in summary, I think the V-Force will provide a small increase in power and performance but it is the increase in torque (if any) that is more important and any differences can probably only be measured in reality against the clock.
Sorry for the long post!