I've been using K&N Filters for over 10 years, and my experience with them is very good. I still have a (I bought it new)93 Escort Gt and I bought the filters on the first service date, I still have the filter same filter, I just take it out every 3 months to clean it. My car response was improved with it.
Ok I bought a 2001 5.9 4x4 Ram 1500 last Nov. I installed the filter 2 weeks ago and I do notice an improvement on my mpg. I travel a lot, about and with the gas prices going up every day, I keep my eye on the mpg of my Tazmanain Devil
On thing about K&N if you take care they can last many years, so you pay big bucks today, but you'll save $ on the long run.