I use the PS/2 port with my Logitech Optical mouse because my backup program runs in DOS, and there is no such thing as a USB DOS mouse driver. The backup program (Drive Image 5) is impossible to use in DOS with some kind of pointer.
The Sample Rate with the mouse is only 100 (60 default), versus 125 with the USB port ... but I can't tell any difference in the tracking. The optical mouse just isn't as good as a ball mouse in that respect. However, that might change, if I can ever purchase a <i>cordless</i>, dual-optical mouse. I expect to see one from Logitech in a few months or so. The regular "wired" dual-optical is already available.
Toejam31
<font color=red>My Rig:</font color=red> <A HREF="http://www.anandtech.com/mysystemrig.html?rigid=6847" target="_new">http://www.anandtech.com/mysystemrig.html?rigid=6847</A>
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<font color=purple>"Procrastination on your part does not constitute an emergency on my part."</font color=purple>