Clean your K&N!

[84LX89GT]

On a daily driven vehicle (one i'd plan driving many miles) i would never own a K&N/cotton gauze filter just because of the fact that over oiling does contaminate the MAF sensor wires and because the cotton gauge filter gets dirty just as fast as a paper filter, also because it flows more air it also flows more dirt into the engine. On diesels owning a K&N filter will eventually "dust" the turbo and cause the seals to leak and the turbo looks sandblasted (Ford denies alot of warranty claims due to those filters on diesels).
MAF sensors are cleanable, but if you don't clean it, the wires could be contaminated and cause it to run lean - if you're not careful and floor it even though you hear pinging it can damage valves and pistons.
To each their own, i'd rather remove the silencer, open up the airbox opening and use a paper filter on my daily driver than have to worry about cleaning the filter and MAF sensor and getting all kinds of dirt into the engine (i drive on a lot of dusty roads).
I had a BBK fenderwell induction system on my GT and loved it, but i only drove that car 14,000 miles in 2 years.