I've recently removed my Injen cold air intake system (CAI) and noticed a drastic increase in fuel economy.
Mind you, with the OEM air box back in, no more VTEC roar at 5.5k RPM or audible air suction sound. Matter of fact, you can't hear VTEC engagement at all unless you turn off the stereo and listen really carefully for it! That's not the interesting part. The observation that caught my attention is the fuel economy. And it appears to have been increased with the OEM air box back in place. Increased drastically. I'm currently at half tank without the Injen CAI and the trip meter reads 200 miles. This is combined city and highway driving. At half tank with the Injen CAI, I usually clock in at around 140-150 miles. So to validate my observation, I'm going to run a couple of tests. I probably won't have results for another 4-5 weeks after doing 3 full tank to empty tank trial runs.
PS - If anybody wants, I'm selling my used Type-S specific 02-06 Injen cold air intake for $175.00 shipped (48 contiguous states). All hardware and a Hydro Shield is included. It has been on the car for a little over a year.