Doing yoga in the nude is becoming increasingly popular, and it's not just some naked stretching in your living room. Though not quite mainstream yet, nude yoga classes are being offered in diverse settings, including yoga studios and community centers, as well as through private clubs. As you might imagine, the venue of the class sets the tone and helps determine the clientele. There are many different motivations for trying nude yoga, though a common thread is developing an acceptance of the body in its natural state. -- http://yoga.about.com
This brings up the whole nudist idea which i'll talk about later but as for the whole 'acceptance of the body in its natural state' how many of the guys believe that as if they are not just there for the women. I think all the erections would be the give away.