NVIDIA decided to forbid manufacturers to overclock the GeForce 8800 graphics cards. Even the watercooled G80 can't get around this:
It would cause bad publicity and a lot of returns. One of the big problems is that there are not enough chips even for current supply, not to mention how long you would have to wait for RMA on a massive scale.
The decision has been made - all Geforce 8800 GTX and GTS remain at the default clock, but coolbit.reg still works. So the end user can have a bit of a fiddle if he or she really wants to.