I installed the V2 cold air intake from smart madness about a month ago, and am very happy with my purchase.
Throttle response and a small horsepower gain are noticeable, but that doesn't really matter to me.
I frequently take a weekend trip from Albany to Rochester, NY to visit family, and the 240 mile trip is a good, consistent basis for comparison. With my trusty Scangauge II hard mounted overhead and cruise set, I have noticed anywhere from 1 to 5 mpg higher numbers since I installed the cold air intake, averaging to roughly 2 mpg increase over what I was getting prior.
Granted, this is not a magic bullet, and by going around 16 miles more per fillup, this will take a long time to pay for itself, but I'm stopping at the pump less, and that's all right with me.