i have to attest to the fact that between removing my airbox and having the K&N installed, there really isn't a noise/performance difference. over stock i'm sure there is. i gained 9hp or so just from the airbox removal.
the good thing about this intake is that i've noticed the car running MUCH smoother than with my filter hanging there next to the engine/tranny. it used to be when i let off the gas, i'd get a rough feeling/jerkiness from the car. with the intake on, it's nice and smooth. i think K&N did a nice job.
as was stated before, you can't really expect TOO much from an intake, but once other mods are done to the car to improve power, the intake will help them make more power because it's flowing more than stock. you can get the same effects with the stock setup, and i'm sure set up like a ram air, it may be even better than the K&N, but it's for looks mostly. if anyone wants an intake, the K&N is the way to go. if you're scared about hydrolock, it isn't going to happen with this intake. the filter sits so high in the fenderwell it's almost funny, not to mention they include the Drycharger with this kit, so it's double protected.
though i do agree that manufacturers play with numbers until they're happy, i believe it all depends on the dyno and the conditions. as long as you try and stay consistant when dynoing gains from mods, you get a realistic view of where you're getting, but you'll never truly know how your car will perform when driving on the freeway, where the power will likely be more of an increase over sitting still on a dyno