In my experience, people can stiff their wrist when they are balanced. If they're busy regaining balance they usually can't put much strenght in their wrist.
Your right...with this one guy I was relying on just bending his wrist and not so much on taking his balance - which I suppose would be a wise practice with each aikido move?
One problem I have is that Im trying to be careful with the uke.
Like yesterday I went to do Kotegaeshi ura.
As I spin around, pulling ukes arm down to take balance - the uke decided to play around and 'escape' from the technique. (again this is not the norm, but sometimes they 'horse play' - of course its not when sensei is looking. I know, it sounds like a kindergarten the way Im describing it.)
But again, he was able to get out of the move, as when I do kotegaeshi ura I try to be careful as not to mess someones wrist up.
I know from experience when your going fast in one direction and then nage turns around rips your wrist in the opposite direction...if your not ready - it hurts.
So some of the problems are stemming from the lower grade belts 'horsing around' and not understanding why the rules of the dojo are there.
Anyway...great comments from everyone.