Why the JIG doesn't work and how to make it work
The JIG that is commonly made/sold is a partial copy of Samsung's Anyway JIG BOX. It copied the box by putting a 301K resistor across pins 4&5 of the micro USB pins. This became well known.
The Bootloader was changed so that the presence of the Resistor is checked for during a short period immediately after flashing and ( I think ) it requires the USB power to be present.
If you make a USB to Micro USB cable with the 301K resistor in place as usual ( pins 4 & 5 ) and connect this to your PC and to the phone, the the JIG Cable will work with the current new style bootloaders exactly as before.
The nice thing is that it is now easier to make as as the micro usb was difficult to open and solder .. but the USB end has more space.
If you want to know more look at the Fairchild FSA9280A-88 Datasheet & 3200
Samsung Galaxy S2
Unlocked & Rooted
Carrier Orange UK
Formerly G1 running CyanogenMod 6.1