Thanks for the comments, guys.
Zeff - the simple answer would be...try it while trying to protect your face with your hands, and then the other way, and notice how much more you bleed and hurt when you're trying to use your hands to protect a relatively small (inefficient) area of your body.
As for getting into that kind of thing...ya just gotta remember, your primary goal needs to be MOVEMENT, just ANY kind of movement until you get your bearings...the goal can simply be "I don't want to be where I was a second ago" to start with. That takes care of most of the stomps that people will try to get your face and limbs with.
After that, to really get over that primal fear of getting hit all over...well...get hit all over. Hard. Lie in a vulnerable position, and over a month or so of training, have someone work up to full speed, full strength kicks to everywhere on your body. You will literally not have the choice to move wrong, your body knows enough to prevent you from doing most really dumb things - trust in that. Just have the objective to RELAX, RELAX, RELAX. Be calm. It's hopeless and it hurts and it's scary when you've just been ambushed and you're being kicked by a lot of people at the same time, but RELAX and you'll have a good chance of coming out relatively okay.
As a sidenote, that drill was done without clueing me in first...i.e. a relatively unexpected ambush. You can see that by the time my mind catches up to what is going on, I'm already out (that's the first thing I remember after "ow")...of course, it's a drill, and I dive back in, but the fact remains...in real life, I would have been out and running...my body took care of the initial evasions and absorption. Just trust that your body pretty much knows what to do and train for what happens in real life. When you get to full speed and power hits, use your breath to cushion hits to your torso. ALWAYS BE RELAXED.
Bamboo - well, "the thick" is what we train for...so I've really become used to it. The first thing every one of our guys says once he's used it for real is "holy shit! This stuff is WAY easier in real life than in class!!!" And that's coming from people who've survived some pretty "hopeless" situations.
As for how often we do that kind of thing...I suppose we start off someone new slower, with less power, so he can get used to the feeling of fear and hopelessness and some pain...then we'll teach the absorption, and how to turn that into using the energy from the kicks to escape and/or break whoever is attacking you. So really...every class I can remember has had "hopeless" reality skill drills in it, but depending on the experience level of those you're working with, you may go lighter, medium, full speed/power, whatever. At the same time, it's a containment/teamwork drill for the kickers, which I find tremendously useful. Once the guy on the ground gets used to taking hard hits, it also becomes a drill for him to REALIZE where he's being contained, and to prevent the attackers from getting into advantageous positions.
If I'm not mistaken, you also do/have done small-circle work. Think of the absorbtion as internal small circle work...i.e., you make the circle with tiny muscle contractions and your breath. It's a very clean, natural feeling when you're getting kicked, and takes out like 90% of the 'bite.'
Hope that helped. There should be more video in the very near future.
-Dave