I've been bantering back and forth with folks at sethigherstandards.com on the pros and cons of nose breathing- breathing in through your nose and exhaling out your mouth while running. While I believe the general consensus is you can't sustain nose breathing while racing or exercising at high intensity, there seems to be several who practice this technique while running a sub max levels and believe in it's virtues.
To be honest, I have never tried nose breathing and have no desire to do so. I'm happy with the way I breath now, exhaling every other time my left foot strikes while running at high intensity. During slow, easy paced recovery runs,who cares?
I thought about it while swimming today- now there is an endurance sport that simply would not allow breathing in through your nose. Same as running, at least in my humble opinion. This is one that can easily be proved or disproved in a laboratory setting. To my knowledge, that's never been done.