From what I understand (having read other Forums and Evga Web Site), some PSU's, even equipped with SLI Ready Power (both 6 pin and 8 pin) are still having issues with the 8 pin, as the 8 pin on some PSU's are not "centered appropriately to match the 8 pin input on the GX2"!
With that said, "apparantly" all GX2 shipped from Evga, will come complete with a 8 pin adapter.
I'm in the middle of "pondering" stepping up from my 8800 GTX to 9800 GX2 ($145) with Step up Program, I am somewhat concerned over the "Heat Issues" as a result of the GX2's not exhausting efficiently.
My PSU is a PC Power and Cooling 750W, but I'm not sure if I would require modifying the pin or not.
Introducing me n my OCD to Watercooling, is like taking an Alcoholic to an "all you can drink" Beach Bar in Mexico