Are the falls in Aikido acted or real? I mean is the attacker forced to fall by action of the attacked or he falls out of his own will?
I think the premise is that ukemi refers to moving because you have to; not necessarily because you're made to...if that makes any sense. "Falling" isn't a bad thing. It's just different and in some cases might simply be the best option. Good ukemi as I understand it means we're maintaining a consistant effort based upon the skills of our partners and ourselves. Sometimes this means letting a person knock you over so they know what it's like to extend completely through the technique; sometimes it means only moving if they've really got control over your center.
One thing that has really been brought to my attention lately is the level of talking that goes on at my dojo. Not everyone likes to be corrected; some I'm sure prefer to go at their own pace, but almost all the experienced students give tons of feedback on what they're perceiving in the movements being practiced. Of course it needs to be balanced with practice itelf so we can move without the prompts, but I think communication helps keep things honest.
We also get a lot of open mat time where we can be more free flowing, which also helps tremendously on keeping ukemi more spontaneous and genuine and less contrived (eg-what happens if they don't let go at the end of a throw?).
As a side note, i think the graduated randori system of Shodokan does a great job of providing this kind of spontaneity.