No G75 units have shipped with Thunderbolt. Despite what you see in the videos on the net, in some reviews on the net, and even with that little lightning bolt on the side of your computer above the port, it's not Thunderbolt. There is no Thunderbolt controller on the motherboard, so that port is ONLY a miniDisplay Port. This has been confirmed by ASUS, search these forums for a thread and you'll see confirmation posts from MarshallR@ASUS.
A future model of the G75 will ship with Thunderbolt, but that has yet to be announced.