I've had great results doing this on a previous vehicle, and I only do it on vehicles that have an ideally located air box, away from heat, and at the front of the engine bay.
Here is a thread I created when I was quite a young bloke, and it's still going today: http://forums.vwvortex.com/showthrea...ation-write-up
It's essentially ram air. I picked up a spare air box from a Miata.net member, just because I didn't want to hack up my own. For what it's worth, it probably sounds better than a cold air intake. Not going to argue performance over a cold air here--I love cold air intakes on the right vehicle, but when you have an ideally placed air box, this could very-well be better, especially because you don't deal with all the extra intake travel that cold air intakes have.