When I rig a piece of clothing, if I miss to 'memorize a pose' before adding the piece to the library, when I bring it back, it doesn't conform right.
When I memorize a pose, it works fine.

My question is, what exactly (technically) does memorize a pose do? I seem to be having brainfarts and not seeing it in literature, tuts etc...  Would someone be so kind to clue me in?

It sets the initial values of the parameters. For conforming clothing these should be zero rotation and translation throughout.

Thank you very much Phil C :)

ooh, I see, sort of telling the rigged object "this will be your zero pose"
And it's different from joint parameters that show in joint parameter editor.
Am I understanding that right?

It is the pose that the figure adopts when you Edit >>>Restore>>>Figure.

When you conform clothing to a figure Poser takes the figure's pose and applies it to the clothing. However to be more exact it adds the figure's pose to the clothing's memorized pose. This is why the clothing's memorized pose must be zero. If it isn't, you'll continually get an offset when the clothing is conformed to the figure.

Quote - However to be more exact it adds the figure's pose to the clothing's memorized pose. [quote] 
AHA!  that's exactly what I thought, or what I was hoping to get confirmed. Now all the puzzle pieces in my head fit!
THANKYOU THANKYOU THANKYOU :)))