To shed some light on the subject without stirring the pot here... The K&N air filter system works on two principals.. first is the fact it lets more air though. It does this through a coarser filtering medium. Second, for those of you that use a K&N filter, servicing it should only take place about once a year... and by servicing it, I mean cleaning it. For upkeep, all you have to do is knock out the large particles and debris followed with a LIGHT coat of the specified air filter oil. By NOT cleaning it, you leave some of the fine particulate on the air filter... its called "caking" and it's imperative for the "proper air filtration" to take place. With said caking on the air filter, it will ACTUALLY filter the air as good as an OEM air filter.
Now, with the above being said about caking, once that has taken place, there is no advantage to running the K&N air filter except for one thing.. ENVIRONMENTAL IMPACT. You can reuse that air filter for a good portion of the life of your vehicle... not to mention the ca$h you save by not buying a new air filter.
Ok.. I have said it. That doesn't mean that I approve of using the above mentioned air filter... all I'm doing is putting the facts out there.
And for those that say they use them in off road racing... well.... some people do, but not without using a pre-filter sock over it. If it were me... and I was running in dusty conditions, I would be adapting a Donaldson style heavy dusty air filter canister. (works on cyclonics).