I waited until my F-150 had 125,000 miles on it to get the K&N filter for it and now wish I had bought it sooner.  The engine response on acceleration improved noticeably, while gas mileage only improved very fractionally.  I like it a lot, but understand that cleaning and re-oiling it will not only be a chore when the time comes, but it might also be a bit pricey (almost as much as the original filter.)  Considering this costs about 2x what an air filter at Jiffy-Lube costs, maybe that's ok, and I'll reserve judgment until I've actually done the cleaning and re-oiling once.  In the meantime, I have smoother, quicker acceleration, and I'm pleased.  I used 4-stars instead of 5 because of the cost/work of cleaning....