Actually K&N claims the filter actually filters better when it gets dirtier (I dont know, it beats me). I have a K&N filter on my Integra and I have noticed no difference besides for it is louder. The intervals they recommend for cleaning the things are crazy, the box says cleaning is recommended between 50k-100k miles for street driven applications. Well I cleaned mine at 30k and it was a pain in the arse to clean 30,000 miles worth of dirt. It took me about 2 hours to "service" the filter, also the kit that I used to clean and oil the filter cost me $20. If I had to do it over again I would have never bought that filter and just stuck with stock.
2003 Volkswagen Golf GL 24,000 miles. 1.9L I-4 TDI 5spd.
1986 300E. 115,000+ miles. 3.0L I-6 1st daily ride, around town only. (Gone)