I've had iOS 4 GM since it was "leaked" but have not been able to convince AT&T to enable tethering. Thinking "launch" day is upon us, I took a gamble and called to see if anything has changed, and sure enough, AT&T turned tethering on for me. Seeing as I work on a military installation and wi-fi is strictly forbidden, this makes all the difference in the world to me. So nice to have a legitimate tethering option without having to jailbreak my phone. Hope someone else is able to benefit from this information as well.