After a short period of inactivity, I've finally got the USB -> Serial converter permission issue sorted! For those of you using Debian Sid (I'd assume not many!) this is the solution...

 # ID 0557:2008 ATEN International Co., Ltd UC-232A Serial Port [pl2303]

KERNEL=="ttyUSB*", SUBSYSTEMS=="usb", ATTRS{subsystem_device}=="0x0557", ATTRS{subsystem_vendor}=="0x2008", MODE="0777", NAME="ttyUSB0"

Then create a file in /etc/udev/rules.d/50-ttyUSB.rules and past the above into it, restart Udev and your good to go!