It's not sure what justifies the extremely high price of this graphics card. A leak from Dell earlier this week indicated that the clockspeeds of the G80 Ultra are only slightly higher than the GeForce 8800 GTX. It's possible that the GeForce 8800 Ultra has other tricks up its sleeve like more shader processors but nothing is really certain yet.
It's also said that this will be a limited edition and that not all NVIDIA partners will get these cards. However, we won't have to wait much longer as the first units are already expected next week.