if you're using single plane polarization yagis for the sats it doesn't matter what that polarization is ssince the satellites are not fixed...
But some satellites are magnetic stabilized to the earth's magnetic field and so these satellites are horizontally polarized nearer the equator and vertically polarized near the poles. And very predictible in between.
On the RAFT re-entry web page are two horizon views of these changes in polarization for such spcecraft. The two views are about 30% down the page:
http://www.ew.usna.edu/~bruninga/craft/save-raft.html
A correllary to this is that when these satellites are due south of you (in the N hemisphere) the antenna is pointed right at you, so you are in a null and signals are weak for a while...
Bob, WB4APR