I imagine that "going with" a technique is a part of any martial art's training. When I studied Kenpo, I remember that we wanted to react as if we had felt the full power of a punch or kick. So, we would exaggerate the effect. This simulation helped the other student learn the proper motion involved with cause and effect. That way, the technique became more natural and applicable to a real situation.
Aikido seemed over the top, though. When I first started, I was told how to move as an uke. The problem for me was that it didn't seem "natural." My inclination was to end up with "this" foot forward, rather than "that" foot, which was the proper one for the technique. It seemed bizarre. Moreover, it seemed kind of fake. I figured to make Aikido work, I would have to find those gems hidden amidst the rocks and integrate them into what I already knew. And I found many gems. Indeed, I found enough of them that I knew this was the art I ultimately wanted to study.
Back then, I only studied for about three to five months before I had to drop the class. It took me thirteen years to find another Aikido instructor. I've been studying it here for a bit less than two years now. Upon arrival, I had the same impression. My job as uke was to help nage to learn the technique, so I went with, and then some. I tried to give the right amount of energy, and I tried to position myself appropriately for the technique to "work." That has changed, though.
As I work with people trying out the art for the first time, I remember what it was like to be moved in my earliest days. I remember some techniques making me to think, "wow, this could end up in face plant quickly. Even the other day when I was briefly loaded up for a hip throw (which wasn't finished), I remember feeling the "oh, shit!" moment as my body wasn't quite sure how to respond.
Is uke "faking" a response? Well, I've come to realize it depends upon what uke is trying to do. If uke is just trying to go through a technique for the purposes of training nage, then I'd say somewhat yes, at least at our lower levels. But if uke is trying to learn how to defend against nage's techniques, then going with will create positioning to open up new possibilities for response. While it might be more natural for me to move with "this" foot forward, putting "this" foot forward may actually put me in greater danger (remember the face plant?). If, however, I move to put "that" foot forward, I may be better able to roll away before being damaged, or to realign my center upon nage for a possible reversal. A while back, Justin had mentioned that at a certain level it becomes harder to tell who is uke and who is nage. I feel like I'm starting to get a glimpse into what that means.
So, with the proper intent, "going with" ceases to be merely about going through the motions (or "faking it"). It isn't just about helping out nage. It's also about training your body to help yourself. Learning how to flow with the energy to reclaim your center is an important part of self-defense. Being uke isn't the opposite of being nage. It's the other side of the same coin.