they still havent realised that when they replace an item on a car that effects performance and sticks on a new "performance" part, the increase they seen is probably very similar to that if they had just put a new part on.
and considering golfs are getting very old, its not suprising "my new K&N makes the car go faster".
anyway, who in their right mind spends money on their car and doesn't get a performance increase? its a p-e-n-i-s thing i think.