In response to Kingfisher's skepticism.  It's important to keep in mind what the goal or goals are in breathing because they would be somewhat different for someone doing yoga or a meditator as opposed to someone engaged in intense aerobic exercise.  I also do a regimen of intense aerobic exercise (not to the puking stage mind you) and would agree that nose breathing is probably not going to happen when you get at or near the wall.  But with regards to intense aerobics the main issue is oxygen exchange.  So the key there is to be doing deep diaphram breathing (which means breathing like a baby where one's belly is working like a bellows.)  Contrast that to how most of us, especially men have been taught to breathe.  Like in the army we suck in our gut and stick out our chest.  That guarentees a shallow breath (just the upper part of the lungs) and minimum oxygen exchange.  When it gets to the short strokes I don't think it much matters whether you're breathing through your mouth, nose or ears.  What matters is breathe control and the extent of oxygen exchange.  At that point the critical issue is the depth of the breath which means maintaining deep diaphram breathing especially as we become more and more fatigued.  Since deep diaphram breathing is how we're born to breathe it is not something we have to learn but rather re-learn.  Once we get the rhythm of it and practice it a bit it becomes second nature not only in intense activities but in every thing we do.
Now just so I'm clear - I am right and I'll definitely put a hurt on anyone who says otherwise!  Now hit the floor and give me 20!