I have used K&N in most of the cars we have owned over the past 7 years and most recently installed one in my 2005 SAAB 9-2X. Besides the improved gas mileage (typically 1 mpg over a new stock filter), and the other benefits mentioned by other users, one area that it helps that no one mentions is protection from rodents! We live in a heavily wooded area, and before using K&Ns, I would often find that mice had made nests using the paper from conventional filters, thereby destroying engine protection provided by the air filter. Mice & chipmunks have really plagued our cars, even eating the top of the gas tank on my wife's new SAAB last spring. (not covered by warranty). They never seem to touch the K&Ns, even in my old MG that sits all week until I drive it on weekends. Must be the combination of a strong wire mesh protecting an oiled gauze that they find distasteful.
Joe Dufresne, Holden, Massachusetts