Hi,
I have had my K&N Filter in for about 500 miles now. The bike runs sweet (once it warms up). But it ran sweet with the old factory filter anyway. The bike is all stock except for the snorkle being removed from the air box.
I paid 50 for the K&N with the cleaning kit included. The stock filter costs any where from 20 to 50 dollars and you have to throw it away every 10k miles. It seems that the K&N is a bargan over the long term.