I ran a K&N on my 94 Dakota V6 from ~15K until I traded it at 49K. When I removed the factory element(Paper w/a fiber "sleeve" around it) at 15K, I noticed a sparse, very fine white dust on the black steel housing bottom, inside the filter. Wiped a finger on it, & got a light coat of white, brown, & black very fine dust! Hmm..Cleaned it all up, installed K&N. Pulled & cleaned it at ~30K- no dust showed up on the "wipe test". Again at 45K-ditto. It seemed to be doing better than the factory paper in cleaning the air. Never saw any difference in power or gas mileage w/Dakota.
Bought Neon 7/97, drove lots, changed paper panel element every 12K miles. Never noticed much dust inside at all-nothing like Dakota had, but still a small trace. Installed K&N last spring ~84K, wiped out housing & pipe as best I could. Just cleaned it a few weeks ago, ~109K. Tried the wipe test as far up intake pipe as I could reach-no visible/feelable dust on finger.
Also,throttle response has been a little crisper, & gas mileage more consistent from tank to tank, for a bit better overall average w/the 5 spd Neon.
So, IME, a *properly cleaned & oiled* K&N seems to have cleaned the air better than paper elements. My advice? Follow the directions when cleaning, *BUT*: be sure to let the element *Dry Completely* before re-oiling. This may take a day or so, & I believe a lot of people get impatient here. I just saved my paper elements, & ran them for a day or two while the K&N dried in the house.
There are some articles floating around on the I-Net saying that oiled cotton filters let too much dirt in. Maybe so, but my experience seems to indicate the opposite.