I was actually the one who started that thread where Ockham posted, haha. :]

 What I'm trying to say is..  I did use IK just to prepare the keyframe poses. I took 2 frames ONLY. First frame start position, second frame with IK on I leaned the person's weight on one leg. Now scrolling between those two poses, you can still see that the feet are moving slightly, so you just know that there's going to be jitter.

 I went a step further and retimed the animation from 2 to 30 frames, and there's the jitter!

 I then saved the animation, loaded a new scene with the figure.. IK off, loaded the animation.. Still the same problem.

Here's the quote from Ockham in the other thread:

"The jittering is a common problem.  There are usually two or three possible
solutions to each IK calculation.  One solution may involve (eg) the right knee
bent slightly forward, the other may have the right knee bent slightly backward.
You don't notice the alternate solutions in a still pose, but in an animation
Poser will pick the one that seems closest for each frame.  And the best
solution for frame 10 may have the knee bent backward, then for frame 11 the
knee bent forward, then for 12 backward again......."

 Which I think means that there's no fixing the jitter, it's just the way Poser calculates IK and cannot be helped?