Well, after abouth a month of Aikido, I now have a VERY different world view on being an Uke. I still agree with the things that I said earlier, regarding the appropriate amount of resistance, but I now know that I am now and was a VERY BAD Uke (Bad Uke, Bad Uke).
As my Sensei says...the most important part of being an Uke is being committed to the attack. I have many problems in my Ukeness. For example, I try to adjust my body weight to say on balance, I readjust my body as the technique progresses occassionally, I release my grip too early, and probably worst of all, I anticipate the technique and take Ukemi before the throw is actually executed. Now, this is all after only a month of Aikido and I come from a style where Ukemi is not taught AT ALL, nor are the fine points of being an Uke.
I have plenty of time to learn, but there is much more to being an Uke than I EVER imagined. Being committed to the technique and providing realism means that you perform the grab or attack, follow through, but also allow your Nage to do the technique. The conversation that I had last night with Sensei was enlightening in this aspect. We don't always do the technqiues full speed and we have the advantage of knowing what is coming....a real attacker won't. They theoretically won't have time or know how to adjust their body to regain balance (or in the more advanced techniques, when they readjust, it only helps the technique work better). They will also be grabbing hard and won't let go right away. So we simulate speed and an attacker's lack of awareness by being "committed" to the attack. Resistance comes with time and experience.
And all of this on top of knowing how to fall without getting hurt...because of course, Ukemi is 50% of aikido....
There is just so much to learn.....