I can honestly and truthfully say (with satya in mind) that I practice yoga asana every day. Sometimes my meditation falls off but I do some form of posture work daily. Sometimes it is only 15 minutes and sometimes I am lucky and get an hour and a half, but mostly I am somewhere in between.
Because I have three small children and have found practicing with them around to be an exercise in frustration, I tend to practice at night once they have gone to bed and the house is quiet. I occasionally forget to change out of my jeans and put on something more appropriate. For fear of the "mommy can you sleep with me", I never return upstairs until bedtime to change. I suppose I could practice in my underwear however my practice space happens to be in front of a very large window only a few feet from the street. I am sure that some of my neighbors would be quite entertained I do not feel like finding photos of me doing yoga in my underwear on the internet... but I digress.
As I mentioned I don't always get to change my clothes so I sometimes practice in my jeans. Now if they are of the snugger nature I alter my postures to fit around my clothes. But occasionally my jeans are a bit more warn in and do not limit my flexibility. However it still feels strange, I feel fabric touching me where I normally do not.
This always prompts me to wonder, why people need "special" yoga clothes. Do the Lululemon yoga pants function any better than an old pair of jeans, does Nike or Roots have something that Levi's do not? The answer... is yes!!! Aside from the very well known fact that Lululemon pants have some kind of weird butt lifting technology making even the most unusually shaped butt look fabulous. They do feel better. Not necessarily better than other brands of yoga pants but certainly better than my worn in jeans, or my yoga pants that I bought for $9.99 because they were on sale. They don't last and they make me itch in strange places!
So the point here is that it is not what you were that counts as long as you are practicing. But if you are going to practice, it does help to wear something comfortable and nonrestrictive. I promise you it will make your asana practice less about how your asana looks and more about your asana or other body parts feel!