K&N filters are used extensively in the racing community for two reasons. One is that the manufacturer sponsors the racers. The other is that the filters do allow more air flow. It should be noted that they don't filter fine particles as effectively as quality paper or oiled foam filters. That's not a concern on a racing engine where it will be torn down after the race anyway. Their main concern is to keep the big chunks out. It would be a major concern on a street engine expected to go for 500k.

Jorg