Confession, I voted no but I did use a K&N drop in for years. If you use an oiled filter you MUST (in the words directly from K&Ns tech guys) "OIL SPARINGLY!" I did have it foul my MAF once. I also noticed a fair amount of dirt thru the entire intake.
I recently tossed it and went back to a paper filter. Honestly, I noticed no power difference going back to paper, maybe a touch more power with the paper.