K&N

Had one on my Dodge Neon that I owned as a teenager. Had fine dust after the filter. The engine never skipped a beat and had that filter for 60k miles. But I did notice that the red color was nearly gone and the filter has turned fairly white after 10k miles of driving. The neon didn't use a MAF sensor but used a MAP sensor to meter air, so nothing to foul on there. Still a little concerned over the fine dust so I decided to stick to OEM going forward, since as others mentioned, the benefits are only truly realized at WOT on most modern vehicles. When K&N first came out, the issue was that engineering's priority was to make a car quiet and get the engine packaged into the engine bay and did not do so much to optimize actual intake size and paths. Most modern cars have a very minimal intake (not so many bends and superfluous paths and bellows) and larger ducting than cars before the early 2000's had. So it's pretty moot now a days unless you are running performance modifications that can make use of extra air.