I've never seen any evidence of crap getting past the K&N's on three of my vehicles. I went with K&N because a paper filter was $15 and should be changed every 10-15K (or less) and the K&N were like $45.

Improperly cleaned (too rough, wrecked the gauze) or not oiled sufficiently (it would be hard to not put enough oil on, people usually put too much), I can see a K&N not filtering well. I haven't seen it myself though. I don't drive down gravel roads every day either, so they're not exactly put to harsh use.

I would also recommend not cleaning them too often. They filter better when some dust collects on the gauze, absorbs oil, and provides more surface area to attract yet more dust. The next time I oil, I'm going to use the DIY aerosol spray packs you can get at Ace or most hardware joints. It's too easy for me to over-oil with the squeeze bottle my oil came in.

JMHO, YMMV, yadda, yadda..

 

Someone better let Michael Waltrip know before it's too late...