Updated on Feb 28, 2011 @ 02:34:
To correct a bit what I said below. I still think that the best clothes for teaching and learning martial art is the same clothes as for teaching and learning ballet: tights and a long-sleeved leotard or a catsuit. (And the worst is hakama.) Only skin tight clothes allow to see if the pose, stands, movements, steps are correct and what they should be.
Zentai is not practical because of the hood and gloves, but really spectacular for demonstrations. See the video below.