Well a K&N is reported to flow a bit better than the paper filter which should increase performance. They are servicable (they are a gauze filter impregnated with a filtering oil) the oil (along with the dirt) can be washed away and then they are reoiled. I have installed K&N's in most of my vehicles over the years both cars and motorcycles.
I have found that the drop -in K&N give a little more reving power, good for passing trucks! and I get 1-2 improvement in MPG. Best time to install is after the first oil change - you can feel the difference.
Yeah, I was looking at this on the Bean Garage thing tethered to this site. The description doesn't mention fuel economy, but it increases acceleration and ultimatly increases the "health" of your engine in the long run (or more rather allows it to have less wear&tear from using a regular filter). I was wondering do any of you all know or can explain it's impact on feul efficiency? Or is it more of a "well, depends on how you drive" type idea.