skioff - good link, looks like it has a lot of other good articles that I will be checking out also.
I recently installed a K&N filter on my wife's Honda CR-V and it seems to have helped the gas milage. She had been averaging around 24 mpg and on the last trip to Atl. it got around 28 mpg. I have been unable to tell if there is any difference in the performance.
'97 Honda CR-V