The Red Gator in Virginia
MAC OS X 10.5.6
MacBook Pro (Intel) using an IOGear GUC232A.
Installed the version referenced on the apple.com downloads site.
Installed and restarted.
Using zterm as the test application.
The single device comes up as /dev/tty.PL2303-0000201A and /dev/cu.PL2303-0000201A plugged into the left-hand USB port and /dev/tty.PL2303-0000101D and /dev/cu.PL2303-0000101D plugged into the right-hand USB port.