I hate those K&N filters lol ... Most of the time the nut rounds off for me. But that's cause some other idiot put the oil filter on and tightened it as though it was necessary to prevent Godzilla from being able to remove it. If I installed the filter, I never any issues removing it because I don't tighten them down like that.
Also, just in case I did tighten it down a tad much, I have a nice metal oil filter socket that fits on the end of the filter and works great (except on K&N filters because of that stupid nut).