I put a Mishimoto intake on my car last week and have been putting miles on it over the past few days.
Definite power boost that can be felt not only by the driver but by Fit-owning passengers as well. I don't doubt the 8whp/tq claims of the manufacturer.
There is also a noise boost, which I suspect most folks here would enjoy but unfortunately my wife does not. It's hardly noticeable unless you're in the throttle fairly hard, which is pretty often in a 100hp car.
It's a full, throaty sound, not at all unpleasant, just a bit too intrusive for my wife's comfort.