I got one yesterday for my lan box.
I unlocked the 16p using the techpowerup article and using Atitool I pushed on the first try the clock to 560/580 !! I played WoW for 1 hour, no crash, no artifacts - with stock cooler and fan set to 100%. Temperature was around 70C, with case opened.
I didn't try more, I will install an ATI Silencer before doing that.
I it amazing. My original X800PRO AGP would not reach 520 !
Regarding the people that fail the mod, I am pretty much believe it is an user mistake.
People sometimes are just not able to follow instructions by the book.
I've seen a lot of people on the past trying 10 times and then getting it done. We had recently one example here at AT for the GTO2, the guy said it didn't work until he tried the BOOT CD, which did that automatically for him - user mistake.